INTRODUCTION

“My heart feels like it is pounding out of my chest.”

Dan Reeves, a 79-year-old white male, makes this statement to the pharmacy technician at the counter while waiting to pick up his prescriptions for flecainide and apixaban. He has his hand over his chest and states he feels tired and short of breath when doing any activity. The pharmacy technician requests help from the pharmacist, who notes that Daniel is showing signs of an arrhythmia. A check of his records shows that he is two weeks late for his refill of flecainide, a medicine to treat atrial fibrillation (AFib). Upon questioning by the pharmacist, Dan says the doctor has told him how important it is to take the medication properly. However, he admits that he sometimes forgets to take the second dose at bedtime.

AFib is the most common type of sustained heart rhythm disorder, also called an arrhythmia.¹ It occurs when the heart's electrical activity is abnormal or irregular, usually resulting in a fast heart rate.¹ If the rate does not return to normal, it can lead to stroke, heart failure, or other medical problems.² AFib is a leading cause of stroke.¹

An estimated 2.3 million people in the United States have AFib, according to the most recent data available.³ Given the association between advanced age and AFib occurrence, an estimated 5.6 million will experience AFib by the year 2050.³ It affects fewer than 1% of people under the age of 60 to 65 but 8% to 10% of those older than 80.³ It happens more often in males and Caucasians.¹

Risk factors for developing AFib include the following¹:

• Advancing age
• Chronic Inflammation
• Congenital heart disease
• Endocrine disorders
• Genetic factors
• High blood pressure
• Increased alcohol consumption
• Neurological disorders
• Obstructive sleep apnea
• Underlying heart and lung disease.

Athletes who overtrain in intense cardiovascular sports, like competitive bikers and marathon runners, also are at an increased risk of developing AFib (see SIDEBAR).

SIDEBAR: IS OVERTRAINING TO BLAME FOR AFIB IN ATHLETES?

According to studies, the prevalence of AFib in athletes is about 2 to 10 times higher than in the general population.⁴ Most cases occur in endurance athletes, such as marathoners, and may result from overtraining. In one study, a group of middle-aged men who ran marathons had a higher incidence of AFib than their sedentary counterparts.⁵ The disease also occurs five times more often in aging cyclists (average age of 66 years old) who continue training.⁶ The duration and intensity of exercise correlate to the development of paroxysmal AFib.⁴

Reports cite “irrational” regimens involving overtraining as the primary factors, along with obesity and diabetes.⁴ Treatment consists of removing the physical stress and prescribing flecainide or propafenone.⁷ Athletes may return to training in four to six weeks but should remain on a beta-blocker to prevent recurrence.^8,9 Providers should consider the cardioselectivity of the beta-blocker and the athlete’s sport when choosing a therapy.⁴ Prevention and treatment of future episodes may include a “pill-in-pocket” approach or cardiac ablation.⁷

AFib occurs when electrical impulses in the heart’s upper chambers, called the atria, come from multiple foci, rather than just the sinoatrial (SA) node. The atrial and ventricular depolarization rate becomes rapid and chaotic rather than their normal, consistent firing and propagation (called normal sinus rhythm).^10,11 When different atrial defibrillation waves collide, they cancel each other out meaning no one pacemaker exists. This causes the atrial chambers to quiver, or “fibrillate” instead of contracting in a normal manner from the top of the atria to the bottom. As a result, blood pools in the left atrial appendage (a tissue sack attached to the left atria) which can lead to blood clots. The clots may dislodge from the left atrial appendage, travel to the brain, and cause embolic strokes.¹¹

The atrial depolarizations bombard the atrioventricular (AV) node separating the atria from the ventricle with approximately 300 depolarization stimuli per minute. The AV node tries to prevent some of these depolarizations from reaching the ventricles, but the resulting ventricular contractions become faster than normal and irregularly spaced.¹¹

PATHOGENESIS

In a normal heart, electrical impulses travel in a coordinated way through the heart’s pacemaker, the SA node, through the atrial tissue, and to the AV node.¹³ The AV node slows the impulse before it travels to and depolarizes the ventricles.¹⁴ When the SA node in a normal heart initiates a depolarization wave, it spreads across the atria from top to bottom. Once the cells depolarize, it cannot depolarize again for a while, and this is called the effective refractory period. Immediately after the refractory period, the tissue is in a vulnerable period because the electrical charge of the cells is normalized but the amount of sodium in the cell is too high and the potassium inside the cell is too low. If another depolarization stimuli hits tissue in the vulnerable period, fibrillation occurs. However, this is rare in normal hearts because it is impossible for the wave of depolarization to circle behind the effective refractory tissue to hit other tissue in the vulnerable period. However, when there is a mixing of electrically active and inactive cells together, the single wave of depolarization becomes fractionated into multiple wavelets in three-dimensional space and one of the wavelets can emerge and hit tissue in the vulnerable period.

AFib originates in the pulmonary vein-atrial border 95% of the time because the pulmonary vein contains electrically active atrial cells and inactive pulmonary vein cells that are intermingled.¹² However, in people with longstanding AFib, the stress kills atrial cells, which are replaced by electrically inactive connective tissue, and the anatomic milieu is created to have AFib generated in the body of the atria itself. Patients with AFib may present to healthcare providers with or without symptoms.¹ Patients may experience chest pain, palpitations, a fast heart rate, shortness of breath, nausea, dizziness, sweating, or general fatigue when they have symptoms.¹ The ventricular rate for a patient with AFib is 110 to 140 beats per minute (BPM).¹

When AFib occurs, the heart can usually quickly abolish it on its own but as periods of AFib continue to occur, subsequent AFib episodes last longer and longer until eventually AFib just continues.

Providers classify AFib into five types¹:

• Paroxysmal AFib will revert to normal sinus rhythm in less than seven days with no antiarrhythmic medication or electrical cardioversion.
• Persistent AFib occurs and then persists, requiring intervention with antiarrhythmic medication or electrical cardioversion.
• Long-standing persistent AFib exists for longer than 12 months, either due to failure to attempt cardioversion or failure of cardioversion.
• Permanent AFib is unresponsive to antiarrhythmic medication or electrical cardioversion and continues for the rest of the patient’s life.
• Non-valvular occurs without rheumatic mitral valve disease, mitral valve repair, or prosthetic heart valves.

AFib can be viewed on an electrocardiogram (ECG), which will show an “irregularly irregular” pattern with no discernable P-waves and irregular RR spacing during rest (see SIDEBAR).¹ Failure to detect paroxysmal AFib on an ECG doesn’t preclude having the arrhythmia because normal sinus rhythm can intersperse between the arrhythmic episodes. In that case, a patient may wear a Holter monitor (a small portable ECG machine) continuously for a few days or a patch monitor with 30-day readouts to detect the arrhythmia.^10,15

SIDEBAR: ECG Interpretation 101^16,17

An ECG is a visual representation of the heart's electrical activity. For a 12 lead ECG, six electrodes are placed on the chest and four on the limbs before connecting them to an ECG machine, which produces a readout. A normal ECG consists of a small P-wave, a large and narrow QRS complex, and a T-wave. The P-wave is a small, positive, smooth wave that reflects atrial depolarization, which precedes contraction of the atria. The QRS complex represents depolarization of the ventricles which precedes ventricular contraction. The T-wave follows the QRS complex and reflects rapid repolarization.¹⁷ Abnormal results from an ECG are a sign of potential heart problems like arrhythmias, ischemia or infarction, or even ventricular hypertrophy.

TREATMENT OF AFIB

The goals for treating AFib include reducing symptoms, preventing clots, and reducing the risk of heart failure and other cardiac complications.¹⁰ According to the 2023 American Heart Association/American College of Cardiology/American College of Chest Physicians/Heart Rhythm Society (multi-society) guidelines, patient-specific factors direct the choice of antiarrhythmic agent.² Among those factors is heart failure, cardiovascular disease, or other health conditions. Treatment also varies based on where providers discovered the AFib: in the inpatient or outpatient setting.²

PHARMACOLOGIC AGENTS

The multi-society guidelines divide the agents for treating AFib into rate control and rhythm control medications.² Rate control agents control the ventricular rate when patients are in AFib for better symptom management.¹⁸ Rhythm control medications restore and maintain normal sinus rhythm.¹⁰

PAUSE AND PONDER: What medications treat AFib symptoms most effectively?

Providers may choose from a wide range of medications, with the treatment choice often determined by the patient’s clinical picture and the setting in which the AFib occurs.

RATE CONTROL MEDICATIONS

Rate control medications slow the impulses through the AV node, reducing the rate of contraction of the ventricles.¹⁸ While the number of ventricular contractions per minute decrease (allowing for better ventricular filling with blood during diastole), the RR spacing remains irregular. This irregularity coupled with the loss of atrial contraction in AFib reduces the cardiac output versus normal sinus rhythm. The goal is better symptom control with limited adverse effects. (See Table 1.)¹⁰

Table 1. Rate Control Medications in AFib

Beta-Blockers

Beta-blockers inhibit the activity of the beta-1 adrenoceptor at the AV node, slowing conduction (negative dromotropic effect).¹⁸ Providers may choose from various options, including atenolol, bisoprolol, carvedilol, metoprolol (succinate and tartrate), and propranolol. Atenolol, bisoprolol, and metoprolol are the cardioselective beta-blockers, which means they less potently block the beta-2 adrenoceptors in the lungs.¹⁹ While all beta-blockers can cause drops in the Forced Expiratory Volume in 1-second (FEV-1) in asthmatic patients, the cardioselective agents do so to a lesser extent. Their effects are readily reversed with standard dosing of inhaled beta-2 agonists. All beta-blockers control the ventricular rate, and the multi-society guidelines consider them first-line therapy.²

Non-Dihydropyridine Calcium Channel Blockers

The multi-society guidelines also list non-dihydropyridine calcium channel blockers dilTIAZem and verapamil as first-line for treating AFib.² They block the L-type calcium channel to produce their negative dromotropic effects and like the beta-blockers have negative chronotropic and inotropic effects, meaning they slow the SA nodal firing rate and decrease the force of muscle contraction, respectively.¹⁸ They provide reasonable rate control and improve AFib-related symptoms compared to beta-blockers.² The multi-society guidelines note that dilTIAZem and verapamil are contraindicated in patients with pre-existing heart failure.¹⁸ However, if the signs and symptoms of heart failure are solely due to the AFib and no other underlying diseases, verapamil and dilTIAZem can be used.

The Institute for Safe Medication Practices lists the generic name dilTIAZem on the look-alike sound-alike list due to the potential for confusion with diazePAM.²⁰ The organization recommends the use of TALLman lettering to distinguish the two drugs.²⁰

Digoxin

Digoxin provides a negative dromotropic and chronotropic effects but does not provide a negative inotropic effect. The inotropic effect can be neutral at serum concentration below 1.2 nanograms/mL but can be positive at higher concentrations.¹⁸ Since digoxin slows AV nodal conduction through enhancing the parasympathetic nervous system, it does not work as well in times of higher sympathetic outflow like exercise or stress. The multi-society guidelines indicate providers may use digoxin with other rate control medications because it will not augment the negative inotropic effects of beta-blockers or non-dihydropyridine calcium channel blockers.² The guidelines also recommend digoxin in patients who do not tolerate or have an inadequate response from other rate control agents.^2,18 It is a narrow therapeutic index medication, with the recommended serum digoxin level for AFib being <1.2 nanograms/mL.² Providers should use digoxin cautiously with verapamil, since verapamil is a P-glycoprotein inhibitor and the combination may therefore increase digoxin levels (see SIDEBAR).¹⁸ However, digoxin may be a good initial choice for acute rate control in heart failure patients with AFib since the negative dromotropic effects of beta-blockers and nondihydropyridine calcium channel blockers could induce decompensated heart failure.² If patients start with low dose beta-blockers and digoxin in heart failure patients, as the beta-blocker dose is increased to therapeutic levels (doubled every two weeks until therapeutic doses are achieved) the digoxin level can be reduced.  

SIDEBAR: DIGOXIN IN AFIB: FRIEND OR FOE?

Digoxin is the oldest medication used today in AFib, with records of its use as early as 1250 AD.²¹ Dr. William Withering first described its good and bad effects in 1785.²² Providers still prescribe it today; however, its use has decreased in the 21st century.²³ In AFib, the multi-society guidelines recommend it as a rate control agent.² The guidelines suggest using it with either beta-blockers or non-dihydropyridine calcium channel blockers or as a standalone medication if the other rate control options are not tolerated.²

Digoxin has a wide variety of adverse effects triggered by toxicity. These include arrhythmias, GI symptoms like anorexia, fatigue, and nausea, and central nervous system issues like mental status changes and visual disturbances.²⁴ Elevated drug levels cause the most toxic effects, often triggered by drug interactions. Other antiarrhythmics like amiodarone, dronedarone, flecainide, non-dihydropyridine calcium channel blockers, propafenone, and quinidine may block P-glycoprotein and increase digoxin blood levels as a result.^25,26 Antibiotics like macrolides and tetracyclines may have similar effects.²⁵

According to reports, toxicity occurs in about 13 to 25 percent of digoxin patients.²⁵ It happens more often with blood levels greater than 2.0 nanograms/milliliter.²⁵ While providers may stop digoxin and provide supportive therapy in milder cases, severe cases require digoxin-specific antibody fragments (digoxin-fab).²² Derived from sheep, digoxin-fab is an intravenous medication that works in 30 to 45 minutes to reverse digoxin toxicity.²⁷ According to reports, providers use it in about 20% of cases of digoxin toxicity.²⁸

Other Rate Control Options

The multi-society guidelines recommend amiodarone, dronedarone, and sotalol for rate control, but only in extreme circumstances. Providers sometimes order amiodarone as a last resort in a hospital setting. Still, it should be used sparingly due to its many drug interactions and adverse effect profile.² Dronedarone has a chemical structure similar to amiodarone, except that it does not contain iodine, making it safer.¹⁰ However, the guidelines do not recommend its use in patients with heart failure or permanent AFib due to the risk of death.^2,18 Sotalol is both a beta-blocker and a potassium-channel blocker that also exerts rhythm control properties.¹⁸ While it is a negative dromotropic agent, it can also prolong the QTc interval on the ECG, which may lead to a life-threatening arrhythmia called Torsade de Pointes.¹⁸

In Torsade de Pointes, the ventricles beat in a fast, irregular manner.²⁹ Torsade de Pointes means “twisting of the points” in French. It refers to a characteristic twisting pattern of QRS complexes around the ECG baseline.²⁹ QRS complexes are specific waves or deflections on the ECG, representing electrical activation of the ventricles.¹⁴ Symptoms of Torsade de Pointes may include dizziness, fainting, or palpitations, or it may not present with symptoms.²⁹ The syndrome can be short-lived and self-limiting or life-threatening.²⁹

RHYTHM CONTROL MEDICATIONS

The Vaughan Williams classification system divides commonly prescribed rhythm control agents into two classes.¹⁰ Miles Vaughan Williams, a British pharmacologist and fellow at Hertford College in Oxford, created the classification system in 1970.³⁰ Medications in Class Ic block sodium channels in the heart.¹⁰ Class III medications alter potassium channels.¹⁰ (see Table 2.)

Table 2. Rhythm Control Medications in AFib

Flecainide

Flecainide, a Class 1c agent, is effective in treating paroxysmal AFib in patients without heart disease.¹⁰ However, it can trigger other arrhythmias; the multi-society guidelines recommend ECG monitoring at initiation and dose changes.² Providers should avoid flecainide in patients with structural heart disease or enlarged left ventricles.¹⁰ Given twice daily for chronic use, it also may serve as a “pill-in-pocket” option at a larger, loading dose to convert an AFib episode to normal sinus rhythm.¹⁰

Providers sometimes give patients “pill-in-pocket” prescriptions, which may be taken at the time of an acute AFib episode to return the heart rate to normal sinus rhythm.² Typically, the approach is first tested under the supervision of a provider before the prescription is written for the patient. Providers instruct the patient to carry the dose with them and take it if and when symptoms occur.²

Propafenone

Providers use propafenone, another Class 1c agent, in paroxysmal and sustained AFib.¹⁰ It blocks sodium channels and has weak calcium channel-blocking and beta-blocking properties.¹⁰ Like flecainide, it can cause arrhythmias, and the multi-society guidelines recommend ECG monitoring at initiation, dosing changes, and periodically during treatment.² Providers prescribe propafenone every 8 to 12 hours as a chronic medication. They may prescribe larger doses in a “pill-in-pocket” approach to convert recent-onset AFib to normal sinus rhythm.¹⁰

Dofetilide

Dofetilide is a Class III agent that blocks IKr, a key potassium channel in the heart.¹⁰ It limits the maximum frequency of electrical impulses without slowing conduction through the AV node.¹⁰ It can cause dangerous arrhythmias, including Torsade de Pointes.² As a result, the multi-society guidelines recommend providers place patients under observation with ECG monitoring for three days when starting this medication.² The initial period requires a hospitalization that lasts at least 12 hours after the patient converts to normal sinus rhythm.² The guidelines indicate providers should monitor potassium and magnesium blood levels due to the risk of arrhythmia.² Providers must dose dofetilide based on kidney function.¹⁰

Sotalol

Sotalol, another Class III antiarrhythmic, is a beta-1 and beta-2 blocker.¹⁰ It prolongs the length of electrical impulses to control heart rhythm.¹⁰ Like dofetilide, it can cause dangerous arrhythmias, including Torsade de Pointes.² The multi-society guidelines recommend three days of inpatient ECG monitoring for patients who start sotalol. The guidelines also suggest regular monitoring of potassium and magnesium levels.² Providers must dose sotalol based on renal function.¹⁰

Amiodarone

While amiodarone is more effective at preventing recurrent AFib episodes than sotalol, dotetilide, and dronedarone, the multi-society guidelines recommend these other options preferably for most patients, although it is a first line option (along with dofetilide) in heart failure.² Amiodarone is a Class III drug that blocks both IKr and IKs potassium channels and exhibits rate control properties.¹⁰ It blocks sodium and calcium channels and displays antiadrenergic properties as well.¹⁰ The multi-society guidelines note that amiodarone has a long list of adverse effects and drug interactions, making it a poor choice for chronic therapy.² The adverse effects include thyroid disorders (see SIDEBAR), lung toxicity, liver toxicity, photosensitivity, blue-green skin discoloration, corneal microdeposits, peripheral neuropathy, and the potential for Torsade de Pointes.¹⁶ However, the balance of IKr and IKs potassium channel blockade means it is less likely to cause Torsade de Pointes than Class III antiarrhythmics like dofetilide and sotalol.² Amiodarone (like dronedarone) blocks many CYP P450 isoenzymes and P-glycoprotein. Notable drug interactions include atorvastatin, calcium-channel blockers, beta-blockers, digoxin, fluoroquinolone and macrolide antibiotics, phenytoin, simvastatin, and warfarin.³⁵

SIDEBAR: THE TROUBLESOME ‘I’ IN AMIODARONE

The antiarrhythmic amiodarone comprises 37% iodine (element ‘I’ on the periodic chart) by weight.³¹ The iodine content and the molecule's shape can cause problems for patients prone to thyroid disorders.³¹ Depending on the patient’s susceptibility, amiodarone may cause low thyroid, called hypothyroidism, or a high thyroid condition, called thyrotoxicosis.³¹

Each 200 mg of amiodarone contains 75 mg of iodine, with 7 mg of free iodine released when enzymes process the medicine.³¹ The free iodine is much more than the recommended daily requirement of 0.15-0.3 mg, which leads to iodine overload.³¹

Iodine is critical in creating and processing thyroid hormones T3 and T4. Excess iodine in patients may lead to an overproduction of thyroid hormone, especially in the short to moderate term. Thyrotoxicosis may also occur due to direct damage to the thyroid, which is called thyroiditis.³³ The consequences of thyrotoxicosis may be severe, including arrhythmias.³³ Treatment of thyrotoxicosis depends on its subtype but may include methimazole, prednisone, or propylthiouracil.^31,34

With longer term use of amiodarone, the thyroid produces similar or slightly higher levels of T4 hormone but this T4 is shunted to reverse T3 (rT3) which is biologically inactive, instead of to T3 which is more potent than T4. It is this reduction in T3 that drives signs and symptoms of hypothyroidism in susceptible patients.³¹ The treatment of hypothyroidism is the use of levothyroxine, following guidelines for its use in low thyroid conditions.³³ In cases in which providers stop amiodarone, thyroid function may return to normal.³¹

Dronedarone

Like amiodarone, dronedarone is a Class III antiarrhythmic that blocks sodium and calcium channels and features beta-blocking properties.¹⁰ It resembles amiodarone in chemical structure but lacks iodine. The absence of iodine makes it safer, removing or reducing thyroid, lung, and liver effects.¹⁰ Dronedarone has shown modest benefits for patients with non-permanent AFib.¹⁰ It is contraindicated in permanent AFib or New York Heart Association Class III to IV heart failure.^2,10,18

CONSIDERATIONS IN CHOICE OF RATE OR RHYTHM CONTROL

Prescribers sometimes face difficult choices between rate control or rhythm control. Many factors affect the decision, including the patient’s clinical picture. How old is the patient? How severe are the symptoms? Does the patient have heart disease?

PAUSE AND PONDER: In what situations would prescribers use rate and rhythm control?

The goals of rate control include treating symptoms, preserving heart function, and improving quality of life.¹⁸ Providers prefer this strategy in older patients (age greater than 80 years) with no or mild symptoms.¹⁸ Rate control also may be the only option if rhythm control fails or the risks of it outweigh the benefits.¹⁸ Finally, rate control is more cost-effective due to the medications' wide availability and low cost.³⁶

However, the correct degree of rate control has been debated. Previous sources have recommended a goal ventricular rate of less than 80 bpm at rest in symptomatic patients, but newer recommendations suggest a more lenient approach of less than 110 bpm.² A recent study showed no difference in outcomes with the more lenient strategy, which the multi-society guidelines currently favor.^2,37 As a general rule, all AFib patients should have a ventricular rate less than 110 bpm; those who can tolerate lower heart rates should get the opportunity to see if this reduces their hemodynamic symptoms during AFib. Once a patient’s ventricular rate is below 80 bpm though, further heart rate reductions are unlikely to provide additional value and they should consider a rhythm control strategy.

Rhythm control is preferred in most cases, even though it hasn’t shown an advantage over rate control in risk of death.^1,10 It prevents stroke and improves quality of life but might increase the risk of hospitalization, especially due to ventricular arrhythmias such as Torsade de Pointes.^38,39 Rhythm control is also the best option in patients with a recent diagnosis and in the case of AFib combined with heart failure.² It reduces symptoms and slows disease progress from paroxysmal AFib to more sustained forms of the arrhythmia.² Remember that rhythm control medication is overlaid upon rate control medication, one does not replace the other.

ANTICOAGULANTS

To reduce the risk of stroke in patients with AFib, the multi-society guidelines recommend the use of anticoagulation in select cases.² Determining the need for anticoagulation involves a risk assessment using a scoring system – the CHA₂D₂-Vasc (see Table 3).² In men, a score of 0 indicates low risk, 1 low-moderate risk, and 2 or more is moderate-high risk.¹ In women, a score of 0 or 1 is low risk, a score of 2 is low-moderate risk, and a score of 3 or more is moderate-high risk.² Providers should start anticoagulation in patients with moderate-high risk and consider it in patients with low-moderate risk.¹ When uncertain about whether the benefits of anticoagulation are greater than the risk of bleeding, providers may use the HAS-BLED scoring system; however, the multi-society guidelines indicate it should not replace clinical judgment.² HAS-BLED considers age, renal and kidney function, stroke history, and other factors to determine the risk of bleeding events with anticoagulation.⁴⁰

Table 3. CHA₂DS₂-VASc Scoring Considerations

Providers prescribe direct oral anticoagulants (DOACs) and warfarin for anticoagulation (see Table 4).^1,2 In patients with AFib and no signs of stroke, providers should start anticoagulation immediately.² The standard for patients with a transient ischemic attack or stroke is the “1-3-6-12” rule. Providers should start anticoagulation in 1 day after a transient ischemic attack and 3, 6, and 12 days after mild, moderate, or severe strokes, respectively.⁴¹ This is because there is an increased risk of cerebral bleeding after a stroke for a short period of time and anticoagulation would exacerbate it.

Table 4. Anticoagulants

DOACs

In most cases, providers prescribe DOACs, including apixaban, dabigatran, edoxaban, and rivaroxaban.² Studies show that each is equal to, if not superior to, warfarin in preventing stroke and has less bleeding.² DOACs have fewer drug and food adverse effects, cost more than warfarin, but do not have INR laboratory costs. Dabigatran binds to thrombin (Factor IIa) in the coagulation cascade, and prevents it from activating coagulation factors.⁴² Apixaban, edoxaban, and rivaroxaban are Factor Xa inhibitors and prevent the cleavage of prothrombin to thrombin.^43-45

Warfarin

Warfarin is a Vitamin K antagonist.² Researchers believe it competitively inhibits the vitamin K epoxide reductase complex 1 (VKORC1), which is important for activating Vitamin K in the body.⁴⁶ Without active Vitamin K, Factors VII, IX, X, and II cannot be activated. Warfarin has long been a standard of anticoagulant therapy, although its many drug and food interactions and the need for regular monitoring make its use challenging for clinicians and patients alike.² However, providers still use warfarin for the treatment of AFib in patients with mechanical heart valves or mitral stenosis.² The goal international normalized ratio (INR) for AFib is 2.0 to 3.0 in most cases, except in the presence of certain mechanical heart valves where the INR is 2.5 to 3.5.¹⁰

CONSIDERATIONS IN THE SELECTION OF ANTICOAGULANTS

The choice of anticoagulant depends on several factors. Despite their high costs, the multi-society guidelines consider DOACs first-line therapy due to their advantages over warfarin.² Compared to warfarin, DOACs have lower bleeding risks, fewer drug and food interactions, no dietary restrictions, and require less therapeutic monitoring.² Providers must adjust DOACs based on renal function.² However, warfarin is the only anticoagulant indicated for patients with mitral stenosis or mechanical heart valves.² Multi-society guidelines do not recommend antiplatelet drugs such as aspirin or P2Y12 inhibitors as a substitute for anticoagulants in treating AFib.²

In patients with both AFib and coronary artery disease, the use of an oral anticoagulant can be used alone to treat both. If the patient requires dual antiplatelet therapy (DAPT), after an acute coronary syndrome or the use of a drug eluting stent, but also has AFib, there is a new recommendation. Instead of 6-12 months of DAPT plus an anticoagulant, they recommend a single month of triple therapy, and then 5 months of the P2Y12 inhibitor + oral anticoagulant followed by the oral anticoagulant alone.

PAUSE AND PONDER: What are the recommendations for reversing anticoagulation with warfarin and DOACs?

Providers must also consider reversal of anticoagulation in the case of bleeding. Removal of the offending drug works in some cases, but providers have options in life-threatening instances. They may reverse warfarin by administering Vitamin K and 4-factor proprotein complex concentrate (PCC) in an acute setting.² Reversal of DOACs occurs in only 2% to 4% of cases.² Providers reverse dabigatran using idarucizumab.² Andexanet-α reverses apixaban, edoxaban, and rivaroxaban.² Providers administer PCC, idarucizumab, and andexanet-α intravenously.

NONPHARMACOLOGIC INTERVENTIONS

Electrical Cardioversion

Providers may attempt electrical cardioversion in emergencies or when medications fail to treat AFib adequately.² The procedure is completed in an outpatient facility. Providers place electrode pads on the patient’s chest and back and connect them to a cardioversion machine.⁴⁷ The patient receives anesthesia, and providers administer a high-voltage shock. The shock resets the heart to its normal sinus rhythm. Providers monitor patients for several hours and then patients may go home if they experience no complications.⁴⁷

The multi-society guidelines recommend anticoagulation therapy three weeks before and four weeks after electrical cardioversion if AFib has been present for more than 48 hours (or an unknown period).² The anticoagulant reduces the risk that a clot may be formed during or after the procedure that can be dislodged and cause medical problems.⁴⁸ Even after the AFib is shocked to normal sinus rhythm, it takes a few weeks for the atria to fully start contracting normally again.

Catheter Ablation

Catheter ablation involves the insertion of small tubes directed through the veins to the heart. The ends of the tubes contain electrodes that damage the diseased heart tissue that is causing abnormal electrical pulses.⁴⁹ Heat (radiofrequency ablation) or cold (cryoablation) from the electrodes destroy the tissue.⁵⁰ As a result, ectopic foci or re-entry circuits are eliminated, and normal electrical conduction resumes. Young, healthy patients are good candidates for catheter ablation and the procedure is much more effective in patients with paroxysmal AFib.¹⁰ The multi-society guidelines recommend catheter abation when antiarrhythmic therapy is ineffective, not tolerated, or non-preferred.² Catheter ablation can be curative of AFib in 70% of cases but may take as many as three attempts to fully resolve the arrhythmia.¹⁰ Providers should continue anticoagulation during and after the procedure unless it is clear that the procedure was curative months down the line.²

Watchman LAA Device and AtriClip

In patients who require anticoagulation, but the risk of bleeding outpaces the potential benefits, there are devices that occlude the left atrial appendage (LAA, the pouch on the left atria where most of the clots form in AFib). The Watchman LAA device is placed inside the atria and then opens like an umbrella to block off the LAA. The AtriClip is a clamp that is applied to close off the LAA from the outside of the heart during open heart surgery. In this case, the clots still form in the LAA but cannot get out in the circulation. If a patient is having nonadherence to oral anticoagulation due to bleeding, this is a potential option that a pharmacist could recommend a patient discuss with their cardiologist.

TREATMENT IN THE ACUTE SETTING

Providers in an acute setting order beta-blockers or non-dihydropyridine calcium channel blockers as the first-line treatment.² If ineffective, digoxin is the next choice. Amiodarone is also an option, but only if the previous treatments fail. Providers should not use dilTIAZem and verapamil in patients with poor left ventricular function or heart failure.²

Providers may attempt electrical or pharmacologic cardioversion in the acute setting, especially in unstable patients.² Providers use one of three intravenous medications in pharmacologic conversion. The multi-society guidelines recommend ordering ibutilide if patients do not have reduced ventricular function or risk for Torsade de Pointes.² Ibutilide is a Class III antiarrhythmic available only in an intravenous form that quickly restores normal sinus rhythm.¹⁰ Providers may also order amiodarone; however, converting to sinus rhythm takes longer than other antiarrhythmics (8 to 12 hours).² The multi-society guidelines suggest procainamide as another option.² It is a Class 1a antiarrhythmic that quickly restores normal sinus rhythm; however, the multi-society guidelines discourage its long-term use due to its many adverse effects.^2,10 Procainamide may cause low blood pressure, nausea, vomiting, and a Lupus-like syndrome.¹⁰ Providers should avoid using it in patients with heart failure, and it can prolong the QTc interval, potentially leading to Torsade de Pointes.¹⁰

LIFESTYLE MODIFICATIONS

The multi-society guidelines recommend lifestyle modifications for patients with factors that may influence the disease course.² Providers should recommend weight loss in overweight and obese patients and moderate to vigorous exercise for all AFib patients. The guidelines also recommend screening for sleep apnea with appropriate treatment if it is found. Finally, providers should counsel patients to reduce or eliminate alcohol and tobacco use.²

AFIB AND HEART FAILURE

Several factors complicate the management of AFib in the presence of heart failure.² Providers should consider the degree of left ventricular dysfunction, which determines the type of heart failure and limits the choice of antiarrhythmic.^2,51

The multi-society guidelines recommend rhythm control over rate control in AFib with heart failure.² However, the multi-society guidelines recommend against certain rhythm control agents—namely, flecainide, dronedarone, and propafenone—in patients with heart failure.² Digoxin may be an appropriate choice for rate control, as it has a role in treating both diseases while non-dihydropyridine calcium channel blockers should not be used.² Beta-blockers can be used, and actually provide enhanced survival in heart failure patients, but need to be started with low doses and then slowly titrated up to therapeutic doses.

Besides treating AFib, an evaluation of the patient should reveal whether their profile meets guideline-directed medical therapy for heart failure.² In the case of heart failure with reduced ejection fraction, this includes one of three approved beta-blockers: bisoprolol, metoprolol, or carvedilol.⁵¹ It also includes mineralocorticoid antagonists like spironolactone, a sodium-glucose cotransporter-2 inhibitor, and either an angiotensin-converting enzyme inhibitor, angiotensin II receptor blocker, or sacubitril/valsartan.⁵¹

DIGITAL HEALTH AND AFIB

Smartphones, smartwatches, and handheld devices show promise for uncovering asymptomatic AFib.⁵² In approximately one-quarter of patients with asymptomatic disease, providers do not discover AFib until patients suffer a stroke.⁵³ In recent years, smart devices have provided a solution – ECG monitors. The devices use a technology called photoplethysmography (PPG) sensor technology.⁵² Reflected light from the device measures changes in blood flow from the irregular heart rate.⁵²

Specific versions of the Apple Watch, the Garmin Venu, and the Samsung Galaxy all use PPG technology to look for irregular heart rhythms.⁵² Fitbit also has PPG capabilities in its Charge and Sense models.⁵² A meta-analysis showed that smartphones detect AFib with a sensitivity of 94% and a specificity of 96%.⁵⁴ Sensitivity means that if a patient is having AFib, the device will detect it 94% of the time. Specificity means that in 4% of cases, when AFib is found, it is due to something other than AFib. PPG technology is equally as effective at detecting AFib as a single-lead ECG.⁵⁴ Another meta-analysis confirmed that smartwatches were not inferior to medical-grade devices.⁵⁵

Some limitations of using smart devices in ECG monitoring include the potential for false positives, disparities in access, and the possibility patients will overload providers with consumer data. ECG monitors may incorrectly indicate positives, especially for young, healthy patients.⁵³ AFib patients older than 65 with a low educational and socioeconomic status often do not own smart devices.⁵⁶ Experts also worry about the possibility of consumer data overwhelming the overworked healthcare system.⁵²

Investigators are examining the possibility that mobile ECG monitoring can reduce stroke risk?⁵². A large initial trial of 75-year-old patients using a Zenicor-ECG device twice daily for two weeks revealed a small but significant reduction in endpoints, which included strokes, at five-year follow-up.⁵⁷

Application stores feature digital apps to help manage AFib.⁵⁸ The apps allow patients to record appointments, feelings, symptoms, and questions for their doctors, among other things. App quality varies, and providers should advise patients to check ratings and reviews and provide recommendations.⁵⁸

PHARMACY TEAM IMPACT ON AFIB MANAGEMENT

Nearly 90% of Americans live within five miles of a community pharmacy.⁵⁹ That fact makes pharmacists one of the most accessible healthcare providers.⁶⁰ Pharmacists and technicians can leverage their familiarity with their customers in several ways.

For pharmacists, managing and monitoring anticoagulation is the most obvious intervention that can improve outcomes. Providers and administrators often ask pharmacists to dose INRs for warfarin patients in clinics, hospitals, and outpatient settings. Pharmacists may monitor for bleeding complications, both with warfarin and DOACs.

Pharmacist medication review activities may catch meaningful drug-drug and drug-food interactions in AFib patients. Pharmacists can also monitor for the toxic effects of medications like digoxin and amiodarone and report any observations to providers. Even common agents like beta-blockers and calcium channel blockers may cause troublesome interactions in patients with complicated clinical pictures. Pharmacists may catch these problems and intervene with the prescriber.

Pharmacists can collaborate with pharmacy technicians to improve patient adherence to medications. While technicians may coordinate the adherence programs, pharmacists counsel patients on the importance of following providers’ medication orders and communicate nonadherence to the prescriber.

Pharmacists also may counsel patients on lifestyle modifications. If a pharmacy has a smoking cessation program, for example, the pharmacist may refer AFib patients to it. The pharmacist may also counsel on the need for weight loss or exercise and help the patient set goals.

Finally, the advent of portable ECG monitors allows pharmacists to set up screening programs for asymptomatic or suspected AFib. The AliveCor KardiaMobile is a single-lead ECG that connects through a smartphone. Pharmacists may use it to collect ECGs and triage patients. A cardiologist then confirms any positive result and refers the patient for treatment.⁶¹

Pharmacy technicians may also help manage AFib. Technicians often coordinate medication adherence programs, such as automated refill reminders, medication synchronization, and compliance packaging. Pharmacy technicians can then inform the pharmacist of cases of nonadherence.

Technicians may also coordinate filling pill-in-pocket prescriptions for medications like flecainide or propafenone. They can also use TALLman lettering for sound-alike look-alike medications and place dosing labels on shelving for narrow therapeutic index medications like warfarin or digoxin.²⁰

Finally, technicians can inform pharmacists when AFib patients try to purchase inappropriate over-the-counter or herbal medications. Decongestants like pseudoephedrine can increase heart rate, and herbals like St. John's wort and hawthorn can interact with antiarrhythmics.^62,63 Medications like non-steroidal anti-inflammatory medications, aspirin, and herbals like vitamin E supplements, ginseng, and ginkgo biloba may interfere with anticoagulation.^62,631

Finally, pharmacies can foster knowledge and understanding of the disease by hosting community events in coordination with local healthcare providers. For example, a pharmacy could hold an event during AFib awareness month in September. Pharmacy staff could invite representatives from local clinics and cardiologists’ offices.

CONCLUSION

AFib is the most common type of heart rhythm disorder or arrhythmia, and its incidence and prevalence continue to grow as the population ages. Goals for AFib patients include prevention of stroke, control of heart failure symptoms, and improvement in quality of life. Rate and rhythm control antiarrhythmics can treat AFib. The rate control strategies help with symptoms by controlling the ventricular rate. Rhythm control medications restore the normal sinus rhythm, but providers must carefully choose and monitor them due to their side effects and contraindications. Providers prefer rhythm control agents in many patients due to their ability to reduce the risk of stroke and improve quality of life. Anticoagulation is indicated in cases of higher stroke risk; providers should choose DOACs over warfarin in most cases, except for patients with mitral stenosis or mechanical heart valves.

Beta-blockers and calcium channel blockers are the first choices in the acute setting, followed by digoxin. Providers have limited options in both rate and rhythm control in patients with heart failure. Beta-blockers, digoxin, dofetilide, sotalol, and amiodarone provide options. Pharmacists can play essential roles in managing and monitoring anticoagulation, performing drug use reviews and adherence monitoring, and screening patients for asymptomatic cases. Pharmacy technicians can aid pharmacists by coordinating adherence mechanisms, filling pill-in-pocket refills, and notifying the pharmacist of patients' improper OTC or herbal selections.

Now let’s return to our patient case. Dan’s uncontrolled AFib requires a quick call to his cardiologist, who suggests he go to a local emergency room for examination. The pharmacy staff offers to put his apixaban, flecainide, and other medications on a medication synchronization program with refill reminders. They also suggest that he invest in a digital device that monitors ECG. He promises to go straight to the emergency room.

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INTRODUCTION

Practitioners in all healthcare settings need to understand and respect gender diversity. Pharmacists and pharmacy technicians can play a pivotal role in gender-affirming care by using inclusive language and developing comprehensive knowledge of pharmacologic interventions. The scope of gender affirming care ranges from puberty suppression to gender-affirming surgeries to align physical appearance with gender identity. Gender dysphoria is a very serious condition among transgender individuals that can lead to depression and suicide. Gender dysphoria is not solely internally driven and can be exacerbated by external stressors/stigma. This includes external aspects of experience such as distress associated with misgendering and social norms, social isolation, transphobia, etc.^1,2 It may be treated with hormone therapy and can require lifelong treatment. Healthcare professionals in the pharmacy setting can help these patients by creating a supportive environment that promotes adherence to their treatment. The SIDEBAR provides definitions for frequently used terms in transgender care.

SIDEBAR: Terminology^1-6

• Gender expression: External manifestations of gender, expressed through one’s behavior, body characteristics, clothing, haircut, name, pronouns, or voice. Typically, transgender people seek to make their gender expression align with their gender identity, rather than their assigned gender.
• Gender role: Behaviors, attitudes, and personality traits that a society (in a given culture and historical period) assigns as masculine or feminine and/or that society associates with or considers typical of the social role of men or women
• Gender identity/experienced gender: One’s internal, deeply held sense of gender. For transgender people, gender identity does not match their sex assigned at birth. Most people have a gender identity of male or female. For some people, gender identity does not fit neatly into one of those two choices (e.g., nonbinary). Unlike gender expression, gender identity is invisible to others.
• Sex: The best-known attributes include sex-determining genes, sex chromosomes, gonads, sex hormones, internal and external genitalia, and secondary sex characteristics.
• Sex assigned at birth: Sex assigned at birth, usually based on genital anatomy. AFAB refers to "assigned female at birth," and AMAB to "assigned male at birth."
• Transgender (also TGD, trans): An umbrella term for people whose gender identity and/or gender expression differs from what is typically associated with their sex assigned at birth. Not all transgender individuals seek treatment.
• Cisgender: A term for people whose gender identity and/or gender expression is aligned with what is typically associated with their sex assigned at birth.
• Gender dysphoria: The distress experienced when one’s gender identity and assigned gender are incongruent, often worsened by external factors like misgendering, social norms, isolation, and transphobia. Not all transgender people experience gender dysphoria; being transgender on its own is not a medical condition.
• Transition: The process during which transgender people change their physical, social, and/or legal characteristics consistent with their affirmed gender identity. Transgender individuals may initially transition socially and postpone medical transition. This is especially true for prepubertal children.
• Transgender male (also: trans man, female-to-male): Individuals assigned female at birth but who identify and live as men.
• Transgender woman (also: trans woman, male-to female, transgender female): Individuals assigned male at birth but who identify and live as women.
• Non-binary: An adjective describing a person who does not identify exclusively as a male or a female. Non-binary people may identify as being both male and female, somewhere in between, or as falling completely outside these categories. While many also identify as transgender, not all non-binary people do.
• Embodiment goals: Body qualities/characteristics that a patient wishes to have (e.g. shape, feeling, behavior of body).

Guidelines

The World Professional Association for Transgender Health (WPATH) publishes the Standards of Care for the Health of Transgender and Gender Diverse People (SOC),⁷ which is the main guideline used internationally for transgender health. This continuing education activity is based on SOC Version 8.

The Endocrine Society develops the Endocrine Treatment of Gender-Dysphoric/Gender-Incongruent Persons: An Endocrine Society Clinical Practice Guideline.³ These guidelines establish a framework for the appropriate treatment of individuals and standardize terminology to be used by healthcare professionals. This activity cites these guidelines as well.

Inclusive Language

Everyday language often revolves around the concept of two genders and one sexuality, potentially overlooking diverse identities. Using gender-inclusive language demonstrates respect and acknowledgment of all gender identities while eliminating assumptions. Using they/them pronouns instead of he/his or she/her when unsure of someone's pronouns is best.⁶ Healthcare professionals can demonstrate inclusivity by introducing themselves with their own pronouns and asking patients how they prefer to be addressed. Common pronouns include she/her/hers, he/him/his, and they/them/theirs..⁶ Healthcare professionals should avoid stating that a person is transgender to others unless that is how the person identifies and is comfortable with sharing that information.⁶ Another suggestion is saying “feel free to bring your spouse or partner” instead of “feel free to bring your husband or wife.”⁶

PAUSE AND PONDER: A fellow colleague consistently misgenders a transgender patient despite being corrected. How would you address this behavior while promoting inclusivity and respect in the pharmacy setting?

Physiology

Puberty is the process of an adolescent becoming capable of reproduction. This process involves the hypothalamic-pituitary-gonadal axis. The first biologic sign of puberty is an increase in endogenous gonadotropin hormone-releasing hormone (GnRH).⁷ GnRH produced by the hypothalamus causes the pituitary gland to secrete gonadotropins: luteinizing hormone (LH) and follicle-stimulating hormone (FSH). LH and FSH stimulate gonads to produce sex hormones.⁸ Table 1 compares puberty in individuals with ovaries and those with testes.

Table 1. Patterns of Typical Puberty⁷

ADULTS

Feminizing Pharmacology

The goals of feminizing pharmacology care are the development of female secondary sex characteristics and the minimization of male secondary sex characteristics. Treatments include externally dosed estrogens and antiandrogens. The selection of therapy should include a patient-specific evaluation of patient goals, medical conditions, medication risk/benefit, and economics.⁷

Estrogen promotes feminine features such as breast growth. Antiandrogens diminish masculine features by reducing endogenous testosterone. Examples of antiandrogens include spironolactone, cyproterone acetate, GnRH agonists, and 5-alpha reductase inhibitors.

Estrogen

In gender-affirming care, estrogen (or 17-beta estradiol) used for feminizing treatment is chemically identical to estrogen produced by human ovaries.^3,7 Multiple dosing formulations exist including oral tablets, topical patches, intramuscular injections, and topical gels/sprays. A major safety concern for anyone using exogenous estrogen is the increased risk of thromboembolic events. 17-beta estradiol is generally preferred over synthetic estrogens for the ease of monitoring serum levels and its lower risk of thromboembolic events. For those older than 45 years and those at a higher risk of venous thromboembolism (VTE), the guidelines recommend transdermal formulations. Cardiovascular screening is essential to identify patients at higher VTE risk. Due to multiple Boxed Warnings in the product labeling and potentially significant adverse events, providers should use caution and consider the risks and benefits of estrogen therapy.^3,7

The desired effects of exogenous estrogen include breast development, redistribution of facial and subcutaneous fat, reduction of muscle mass, reduction of body hair, and reversal of scalp hair loss. Exogenous estrogen will not alter voice or height in adults. Table 2 describes available estrogens used in gender-affirming care.^3,7

Table 2. Estradiol for GAHT⁹

Antiandrogens

Antiandrogens, listed in Table 3, can reduce endogenous testosterone levels or its activity and are usually used in combination with estrogen for feminizing effects. While antiandrogens may be employed as monotherapy, combination treatment can help minimize the amount of estrogen necessary for gender-affirming effects and therefore reduce the estrogen-associated risks. General adverse effects of antiandrogen monotherapy may include hot flashes, low mood or energy, and bone loss when used long term.⁷

Table 3. Antiandrogens for GAHT^10-13

Spironolactone is a potassium-sparing diuretic that has many therapeutic uses including in heart failure and hypertension. Spironolactone is also an aldosterone receptor antagonist that can cause positive effects, such as gynecomastia (an increase in breast gland tissue) for transgender women. Gynecomastia is dose and duration dependent, occurring in approximately 10% of patients. The diuretic and antihypertensive effects may become apparent within two to three weeks potentially resulting in excess urination and low blood pressure.^3,14

GnRH agonists (histrelin, leuprolide) work by continuously activating the pituitary gland to make more LH and FSH. This overactivation eventually suppresses sex steroid production. Out of pocket costs for these medications can range anywhere from $10,000 to $50,000 for three months, thereby significantly limiting their use.¹⁶

WPATH does not regularly recommend other drugs like 5-alpha reductase inhibitors, finasteride or dutasteride, as data supporting use in the transgender population is sparse.⁷

Cyproterone acetate is a synthetic progestin that inhibits testosterone synthesis and action. This medication is not approved in the United States but may be used elsewhere.³

PAUSE AND PONDER: A transgender patient presents with concerns about the different formulations of estrogen available for feminizing treatment. How would you explain the advantages and disadvantages of each formulation?

Masculinizing Pharmacology

The goals of masculinizing treatment are the development of male secondary sex characteristics and the minimization of female secondary sex characteristics. Masculinizing GAHT typically consists of testosterone.

Testosterone

Testosterone treatment in transgender patients is used in the same way that it is used for hypogonadism in cisgender male patients. Table 4 illustrates the various testosterone formulations in transgender care, including intramuscular, transdermal, and implantable options. Intramuscular injections may be preferred due to available clinical data, efficacy, patient satisfaction, and low levels of injection pain and local irritation relative to subcutaneous injections. Prescribers and patients should not interchange products without considering pharmacodynamic differences.^7,16

Positive effects of masculinizing hormones include irreversible deepening of voice, increased body/facial hair, and increased lean muscle mass. Patients and care teams should know that masculine hormone therapy will not reverse previous feminine features such as breast tissue. Achieving physiological testosterone levels will usually suppress menses. If testosterone monotherapy doesn’t suppress menses, additional therapies can be used including progestins, GnRH agonists, and aromatase inhibitors. Patients may continue testosterone therapy for life unless medically contraindicated.¹⁶

Table 4. Testosterone Formulations for GAHT ¹⁷

CHILDREN

GAHT is not recommended in children who have not begun endogenous puberty. Healthcare providers should take a non-pharmacologic approach instead for pre-pubertal individuals, including psychosocial gender-affirming care. Patients should continue gender exploration regardless of social transition.⁷

ADOLESCENTS

GAHT’s goal in adolescents is pubertal suppression. Halting progression of puberty allows adolescents to explore gender identity and embodiment goals. Although suppression is reversible, the treatment team should discuss fertility preservation before starting supression.⁷ Current timing and readiness estimates are as follows: pubertal suppression at 12 years old, GAHT at 16 years old, and surgery at 18 years old.

Pubertal Suppression Pharmacology

Healthcare providers employ Tanner staging to track children’s development during puberty. It outlines five specific stages for the physical changes during this period, including genital, breast, and pubic hair development. Patients should reach Tanner Stage 2 before initiating pubertal suppression. In Tanner Stage 2, individuals who are assigned female at birth would experience breast budding while those who are assigned male at birth would experience external genitalia enlargement.⁶ Menstrual suppression is recommended for patients assigned female at birth with gender incongruence, regardless of testosterone therapy.⁷

Pharmacologic Agents

Gonadotropin-Releasing Hormone (GnRH) Agonists

GnRH agonists cause partial regression of secondary sex characteristics and inhibit physical functions, such as menses and erections, by decreasing concentrations of gonadotropin and sex steroid hormones. Supraphysiological doses of sex steroids are not needed with GnRH agonists.⁷

Short-term hypertension is an important counseling point. Individuals who are older than 14 years also have a long-term risk of poor bone health because of the lack of exposure to adequate levels of sex steroid hormone levels. Sex steroid hormone therapy, however, induces rapid recovery of bone mineralization rate.⁶

For feminizing therapy, patients should continue puberty blocking until gonadectomy. Masculinizing pharmacology is covered in the following Hormone Therapy section. If patients have functioning uterus and ovaries, health care providers should counsel on potential breakthrough menstrual bleeding two to three weeks after GnRH agonist initiation.

Progestins

Oral or injection depot progestins are recommended if GnRH agonists are unavailable or cost-prohibitive.⁷

Patients can also receive these progestins if they seek menstrual suppression only⁷:

• Oral progestin-only pills (contraceptive and non-contraceptive options)
• Medroxyprogesterone injection (e.g. Depo-Provera)
• Levonorgestrel intrauterine device (e.g. Mirena, Liletta, Kyleena, Skyla)
• Etonogestrel implant (e.g. Nexplanon)

If a patient continues to have menstrual bleeding after taking progestin and/or is seeking a contraceptive, healthcare providers can consider a combination progestin-estrogen product for amenorrhea and counsel on possible breast development. Combined formulations include oral contraceptive pills, transdermal patches, and vaginal rings. Note that increased breakthrough bleeding is associated with lower dose ethinyl estradiol in combined oral contraceptives.⁷

Hormone Therapy (HT)

The patient’s health care professionals will need to measure hormone levels during gender-affirming treatment. The purpose is to ensure that endogenous sex steroids are falling and the sex steroids administered to the patient stay at appropriate levels. Appropriate levels are determined by (1) the patient’s treatment goals and (2) the patient’s Tanner stage. Timing of pubertal suppression determines sex steroid HT regimen, as shown in Table 5.⁷

Table 5. Sex Steroid Hormone Therapy Regimen Based on GnRH Agonist Treatment Timing⁷

WPATH suggests 12 months as sufficient time for psychological adaptations to physical changes due to GAHT. Healthcare providers should monitor sex steroid levels every three months during the first year of HT or with dose changes. Once the prescriber titrates the patient’s dose to the adult maintenance dose, monitoring one to two times annually is sufficient. As GAHT can activate the hypothalamic-pituitary-gonadal axis, prescribers may need to add a GnRH agonist as adjunctive therapy after GAHT initiation to avoid development of characteristics associated with the patient’s sex assigned at birth.⁷

For masculinizing GAHT, testosterone monotherapy at physiologic doses is typically sufficient to decrease estrogen secretion by the ovaries. Injection, transdermal, and subcutaneous pellets are available androgen formulations. Key counseling points include the possibility of developing androgenic acne or sexual dysfunction.

Patients on GnRH agonists should continue them until they reach maintenance testosterone level. If the patient was not on a GnRH agonist as an adolescent, then no concomitant GnRH agonist is needed. While testosterone usually suppresses menstruation in the first six months of therapy, healthcare providers should make sure to counsel adolescents on possible pregnancy despite amenorrhea because they can still ovulate.⁷

NON-PHARMACOLOGIC INTERVENTIONS

Chest Binders

Chest binding refers to compressing breast tissue to achieve a flatter chest appearance. Research indicates that up to 87% of individuals identifying as transgender males have tried chest binding.⁶ Various methods used for binding include commercial binders, sports bras, layering clothes, elastics, and bandages.⁷

Healthcare providers play a crucial role by making patients aware of chest binding’s potential advantages and risks. Transgender men who bind often report benefits such as increased comfort, enhanced safety, and reduced instances of misgendering.⁷

Negative physical impacts of chest binding include back or chest pain, difficulty breathing, and feeling overheated.⁷ Severe health issues like skin or respiratory infections and rib fractures, which are rare, have been linked to adult chest binding.⁶ Providers can lower the risk by counseling patients on safe binding methods, like binders specifically designed for gender-diverse individuals, to lessen the likelihood of serious health complications. Meanwhile, patients should avoid unsafe methods like duct tape, ace wraps, or plastic wrap due to their potential to constrict blood flow, harm the skin, and restrict breathing.⁶ If negative health effects occur, seeking guidance from medical professionals experienced with transgender and gender-diverse patients is sensible.⁷

Tucking

Genital tucking involves positioning the penis and testes to minimize the visibility of genital bulges.⁷ This can be done by tucking the penis and testes between the legs or placing the testes inside the inguinal canal while pulling the penis back between the legs.⁷ Underwear or specialized garments called gaffs are commonly used to keep the genitals in place.⁷

Research on the risks and advantages of tucking in adults is limited, and no studies conducted specifically address youth.⁶ Previous research has highlighted that snug undergarments might lead to reduced sperm concentration and motility. Moreover, higher scrotal temperatures due to tucking might theoretically impact sperm production and fertility.⁷ However, no conclusive evidence confirms these negative effects. More data is needed to understand the risks and benefits of tucking.

Voice Therapy

Hormone treatment for transgender and gender diverse (TGD) individuals has potential effects on voice and communication. While estrogen treatment does not usually cause measurable voice changes, testosterone treatment can lead to desired shifts in voice pitch and male attributions but may also result in undesired outcomes.⁷

Research indicates that some TGD individuals experience positive effects from testosterone, such as lowered voice pitch and increased satisfaction, aligning with their gender identity. However, a significant portion may face challenges like insufficient pitch changes, vocal quality issues, limitations in singing range, and vocal instability post-treatment.^7,18 A meta-analysis examined about 600 patients across 19 studies to determine the effects of at least one year of testosterone therapy. The patients were all at least 18 years old, with an average age of 35 years. According to the results, approximately 21% of participants did not reach the expected normative frequencies associated with cisgender males. Additionally, a similar percentage reported incomplete alignment between their voice and gender identity, experiencing voice-related challenges or incongruence. Furthermore, 16% of individuals undergoing testosterone therapy expressed dissatisfaction with the changes in their voice.¹⁸

It's essential to provide accurate counseling beforehand to establish realistic expectations and avoid potential disappointment. Referral to voice and communication specialists can address concerns through tailored voice training and assisting those dissatisfied with outcomes or lacking access to hormone treatment.⁷

Electrolysis And Laser Hair Removal

Hair removal is a significant part of transitioning for many transgender women (or females), particularly for those seeking a more stereotypical feminine appearance. The process helps alleviate dysphoria, boosts self-confidence, and enhances overall quality of life.¹⁹ The U,S, Food and Drug Administration recognizes laser hair removal as a permanent hair removal method.¹⁷ It targets melanin in hair follicles using laser light waves.¹⁹ An alternative, electrolysis, also removes hair permanently using a small probe inserted into individual hair follicles to administer an electric current.¹⁷

For individuals undergoing GAHT, healthcare providers need to keep specific considerations in mind. Among transgender women taking estrogen¹⁹

• Estrogen hormone therapy often results in an overall reduction in body hair, except for minimal effects on facial and genital hair.
• The extent of hair removal (complete hairlessness or retaining some hair) depends on personal preference and comfort levels.
• Many transgender women find facial and neck hair removal crucial for increased self-confidence, reduced dysphoria, and a sense of safety in public spaces.
• Those prioritizing gender-affirming lower surgeries like vaginoplasty (vagina construction surgery) require completely hair-free areas for surgery preparation, as hair growth within transformed tissue can cause complications.

For transgender men taking testosterone¹⁹

• Testosterone hormone therapy generally leads to increased body hair growth.
• Preparing for surgeries like phalloplasty (penis construction surgery) often requires completely hair-free skin areas for successful procedures, the specific area depending on the type of surgery planned.
• It is important to note that electrolysis doesn't prevent the growth of new hair follicles activated by testosterone. Therefore, new hair growth might occur in areas previously treated with electrolysis due to testosterone’s effects on stimulating hair follicles.

The adverse effects of hormone therapy may be beneficial for some patients, while being detrimental to others. It is critical for healthcare providers to educate patients on hair removal methods and their impact within the context of hormone therapy, so that patients understand what to expect.

Gender-Affirming Surgery

Gender-affirming surgery is often a crucial milestone for many, but not all transgender adults.³ Broadly classified into two categories, surgeries (1) directly impact fertility or (2) have no effect on fertility.³ Surgeries that alter fertility involve procedures like the removal of male genitalia (penis and gonads) for transgender women or the removal of female reproductive organs (uterus and ovaries) for transgender men.³ Surgeries that do not affect fertility include chest masculinization or breast augmentation, facial feminization, or facial masculinization surgeries.³

There is a lack of evidence supporting the routine discontinuation of hormone therapy before planned surgeries.²⁰ The majority of evidence advocating for estrogen cessation before surgery is derived from studies involving oral synthetic estrogen regimens (ethinyl estradiol), which are uncommon in transgender patients.¹⁹ WPATH advises maintaining estrogen therapy both before and after surgical procedures in transgender women, particularly in those without specific risk factors such as smoking, family history of VTE, or the use of synthetic estrogens.⁷ If the patient has the previously mentioned risk factors, the prescribing endocrinologist should discuss estrogen therapy cessation in the perioperative setting openly with the patient and make decisions collaboratively.²⁰ Typically, an acceptable timeframe for estrogen discontinuation is two to four weeks before the procedure.²⁰ Anticipated physiological and psychological withdrawal symptoms may include anxiety, autonomic hyperactivity, depression, decreased seizure threshold, and fatigue.²⁰ This comprehensive approach ensures a thoughtful consideration of hormonal factors in the surgical process for transgender women.

Evidence suggests that there is generally no need to discontinue testosterone treatment routinely in transgender men before scheduled or elective surgery despite the concern that testosterone can be aromatized to estradiol, which theoretically could increase the clotting risk.²⁰ A recent systematic review found no association of increased VTE complications after surgery with perioperative testosterone use.^21,22

The decision to undergo these surgeries is deeply personal and varies based on individual needs, preferences, financial access, and dysphoria. Access to comprehensive information, counseling, and support from healthcare professionals helps patients make informed decisions aligned with their gender identity and long-term goals while understanding the potential impact on fertility.³

PAUSE AND PONDER: A transgender patient would like to undergo breast augmentation but has only been on hormone therapy for six months. Is she eligible for the surgery?

Chest or “Top” Surgery

“Top” surgery is either removing breast tissue for a more masculine appearance or enhancing breast size and shape for a more feminine appearance. Breast surgery is a type of gender-affirming surgery with no impact on fertility.³ Since breast size varies among females, it is advisable for transgender women to postpone breast augmentation surgery until they have undergone at least two years of estrogen therapy.³ This is recommended because the breasts continue to grow during this period of hormone therapy.³

Meanwhile, the primary masculinizing surgery for transgender men is a mastectomy, which also has no impact on fertility.³ While breast size only partially regresses with androgen therapy, discussions about mastectomy in adults typically occur after androgen therapy starts.³ However, in some cases where trans-masculine adolescents present after significant breast development, a mastectomy may be considered approximately two years after starting androgen therapy and before the age of 18.³ Treatment decisions should be individualized based on the individual’s physical and mental health status. ³

Genital or “Bottom” Surgery

Genital or “bottom” surgery involves transforming and reconstructing the genitalia. According to The Endocrine Society Clinical Practice Guideline Criteria for Gender-Affirming Surgery, the following factors may influence decisions related to fertility preservation³:

1. Persistent and well-documented gender dysphoria
2. Meets the legal age requirement in the relevant country
3. Use of gender-affirming hormones for a continuous 12-month period, unless there is a medical contraindication
4. Successful in living full-time as a new gender role for the duration of 12 months
5. Well-controlled management of any significant medical or mental health conditions, if present
6. Demonstrated knowledge of practical aspects related to surgery, including cost, required lengths of hospitalizations, likely complications, and postsurgical rehabilitation.

Gender-affirming surgeries for transgender women that affect fertility include procedures like gonadectomy (orchiectomy), penectomy, and the creation of a neovagina.³ In the case of transgender men, surgeries that affect fertility include an oophorectomy, vaginectomy, complete hysterectomy, and the creation of a neopenis.³ Infertility can occur from both the temporary consequences of gender-affirming hormone therapy and permanent effects of gender-affirming surgeries (GAS).⁶ It is crucial to engage in ongoing discussions about infertility risks and fertility preservation options with transgender individuals and their families before and after initiation of therapies and surgeries.⁶

OTHER CARE IMPACTED BY GAHT

Anticoagulation

When assessing the risk of VTE associated with GAHT, it is crucial to consider the alternative—the risk of not providing GAHT.²² Withholding GAHT could lead to adverse mental health consequences that might outweigh the risk of VTE.²⁰ Some individuals may seek hormone therapy outside clinical care settings (that is, from unreliable sources) if healthcare providers refuse to provide it.²²

For transgender individuals experiencing VTE while on GAHT, treatment should align with current therapeutic anticoagulation recommendations for cisgender individuals.²⁰ The American Society of Hematology guidelines recommend direct oral anticoagulants (DOACs) over other options due to a lower risk of bleeding.²² Despite limited data in transgender people, recent case reports suggest DOACs are effective in those with VTE during GAHT. In severe cases threatening limbs, clinicians can consider thrombolysis and recommend it as they would in cisgender individuals.²² GAHT discontinuation during an acute VTE episode is often recommended, especially with above normal hormone levels, but this recommendation lacks extensive data.²² Clinicians and patients should discuss the potential risks and benefits of continuing GAHT during an episode.

Following acute VTE treatment, the decision to resume GAHT becomes complex. Many clinicians continue GAHT, even in patients with previous VTE, along with full-intensity anticoagulation to prevent recurrence.²² Although researchers have not conducted systematic evaluation in transgender patients, this approach was effective in cisgender women on hormone therapy.²² While cisgender patients may reduce anticoagulation dose after initial therapy, it is uncertain if dose reduction is prudent with GAHT. Shared decision-making, emphasizing the risks and benefits, remains crucial in determining the course of GAHT post-VTE treatment.

Estimating Kidney Function

Many healthcare providers are accustomed to using the Cockcroft-Gault equation to estimate kidney function.²³ This formula factors in sex, causing uncertainty as to how to calculate creatinine clearance in transgender patients. Although GAHT affects muscle mass and creatinine, using the duration of therapy is unreliable because the timing and magnitude of effect differ by individual. As such, cystatin C is often more accurate than creatinine. Acknowledging that cystatin C levels are not accessible at all practice sites, some experts suggest using the Cockcroft-Gault-calculated male and female creatinine clearance estimates as a range. Other methods include using vancomycin clearance calculations.²³

Fertility Preservation

Individuals who have transitioned may wish to have biological children for personal reasons, to maintain a genetic connection with their offspring, or to conform with cultural expectations.²² While many transgender individuals may not initially consider having children, their desires can change over time.²⁴ In a survey of 50 transgender men who had undergone gender-affirmation surgery, the majority (77%) had not contemplated fertility preservation before GAHT. An average of 9.9 years after starting testosterone therapy, 54% of participants wanted to have children.²⁵ The study also found that participants with children had a higher quality of life than those who did not have children.²⁵

Fertility preservation through the cryopreservation of sperm and oocytes is a well-established technique, available for pubertal, late pubertal, and adult individuals assigned male or female at birth^.6 Ideally, clinicians should present this option before initiating GAHT.⁷ Clinicians can offer embryo cryopreservation to adult transgender individuals, particularly those who have completed puberty, express a desire to have a child, and have a willing partner.⁷

While research has shown semen parameters may be compromised after the initiation of GAHT, a small study indicated that when treatment was discontinued, semen parameters were minimally altered.²⁶ In regards to oocyte preservation, there is no expectation that assisted reproductive technology (ART) treatments would be different for TGD patients compared to cisgender patients.⁷ The only potential variations are individuals with confounding factors related to infertility.⁷

Barriers to fertility preservation include financial constraints, invasiveness of procedures, and concerns about mistreatment or bias from healthcare providers.²⁴ Some fertility preservation procedures, such as sperm or egg collection, can serve as reminders of their sex assigned at birth and may trigger gender dysphoria.²⁴ Transgender individuals who pursued ART reported mixed experiences. Some have positive encounters with supportive providers who use gender-neutral language. Others experienced misgendering in clinical documentation.²⁴ Patients should be provided with options for future family planning whether they desire biological children or not.

BARRIERS IN PRACTICE

Laws and Legislation

When the Supreme Court tackled the Conservative challenge to the Affordable Care Act (ACA), the focus was on whether it was constitutional to mandate health insurance purchase.²⁷ This overshadowed Section 1557's anti-discrimination provisions protecting transgender individuals. The 2016 Rule, finalized by Health and Human Services, extended Title IX's anti-sex discrimination coverage to include "gender identity," ensuring equitable access to healthcare for transgender patients. The Trump administration attempted to reverse these protections but faced legal obstacles. This led to the Supreme Court's ruling in Bostock v. Clayton County, which affirmed protections for transgender individuals under existing civil rights statutes. Despite the Trump administration's efforts, subsequent legal challenges and judicial actions further emphasized protections for transgender individuals, leading to ongoing debates and policy shifts under the Biden administration.²⁷

The Bostock ruling, initially about employment, now impacts transgender minors' access to gender-affirming care.²⁷ Federal courts often interpret Title VII and Title IX together, meaning they see both statutes as prohibiting sex-based discrimination similarly.²⁵ This means that the Biden Administration can confidently enforce protections for gender identity under Title IX, following Bostock's reasoning.²⁷ Since Bostock's ruling was made under a majority conservative Supreme Court, it's unlikely to be reversed. This leaves opponents of gender-affirming care to explore other tactics, like raising religious objections or labeling such care as "experimental" or "medically dangerous."²⁷ These viewpoints circumvent many physicians’ clinical judgement, thus restricting how they practice medicine.

Over the past 18 months, the number of states implementing laws that restrict or prohibit minors' access to gender affirming care has increased dramatically.²⁸ Currently, the count of states with restrictions increased from just four states in June 2022 to 23 states by January 2024. Among these states, 17 have fully enacted their restrictions, while four face temporary injunctions, and one is permanently blocked pending appeal. The laws vary in complexity, with some focusing on specific aspects of gender affirming care, such as GAHT or gender affirming surgery. Additionally, while these laws primarily target minors' access to care, they often include provisions affecting other groups, such as parents, medical providers, and teachers.²⁸ These laws and policies cause potential harm to the wellbeing of young TGD, thus emphasizing the need for continued advocacy and support for inclusive and affirming practices.

Insurance Coverage

Ensuring comprehensive healthcare for transgender individuals requires access to both gender-affirming care and a wide range of inclusive services. However, numerous barriers have historically hindered access, with lack of health insurance coverage being shaped by intersecting factors at the individual, interpersonal, and structural levels.

Many state Medicaid programs exclude coverage for gender-affirming care, posing a significant concern given the elevated prevalence of poverty among transgender people. In a study utilizing Behavioral Risk Factor Surveillance System (BRFSS) data, gender non-conforming individuals were nearly twice as likely as cisgender women to report unmet care needs due to financial issues.²⁹According to the 2015 United States Transgender Survey, 25% of insured respondents encountered insurance discrimination.²⁹ Experiences included denial of coverage for gender-specific services, such as cancer screenings (13%), for care unrelated to gender affirmation (7%), and for gender-affirming surgery (55%) or hormone therapy (25%).²⁹ TGD individuals (33%) reported negative experiences related to being transgender when seeing a healthcare provider in the previous year, which includes verbal harassment, physical assault, or treatment refusal.²⁹ Additionally, 23% refrained from seeking care when needed in the previous year due to fear of mistreatment.²⁹

A 2019 systematic review revealed that 27% (range, 19% to 40%) of transgender individuals reported outright denial of healthcare.²³⁰ Assessments of provider readiness indicate that many clinicians lack training in transgender clinical and cultural competency, potentially contributing to interpersonal discrimination in healthcare settings.

Assessing Implicit Bias, Addressing Bad Behavior

1. Respect Gender Identity: TGD individuals deserve the same respect as cisgender patients. Address patients by their chosen name and pronouns, reflecting their gender identity. Avoid gossiping or making jokes about patients and treat them with the same respect you would want at work.³¹

2. Recognize Workplace Values: Understand the difference between your personal beliefs and the workplace values of dignity and respect for everyone. While you are entitled to your opinions, professionalism requires setting aside personal views and treating everyone with fairness and courtesy in the workplace.³¹

3.Seek Feedback and Learn from Mistakes: Don't be afraid to ask for feedback from TGD individuals about how you can better support them or avoid inadvertently causing harm. Be open to learning from your mistakes and apologize if you unintentionally offend someone. Additionally, take the initiative to stay updated on evolving terminology and practice recommendations, as ideas/norms about gender are fluid and change over time. Learning from reputable sources, such as The Trevor Project's Guide to Being an Ally to Transgender and Nonbinary Youth, shows a genuine commitment to fostering inclusivity and respect in the workplace.^31,32

4. Support Colleagues with Challenges: If you notice co-workers struggling to adjust to interactions with TGD individuals, offer gentle reminders about using the correct name and pronouns. Help them understand the impact of their behavior on both the TGD individual and the workplace environment. Encourage empathy and understanding to foster a more inclusive workplace culture.³¹

5. Intervene When Appropriate: If you witness blatant inappropriate behavior or discriminatory actions with no remorse towards a TGD individual in the workplace, don't remain silent. Find appropriate ways to intervene, whether it's addressing the behavior directly, reporting it to management, or offering support to the affected individual. Standing up against prejudice and discrimination helps create a safer and more inclusive work environment for everyone.³¹

CONCLUSION

Embracing gender diversity and providing gender-affirming care is essential in healthcare settings, including pharmacies. Pharmacists and pharmacy technicians who employ inclusive language and possess a thorough understanding of pharmacological interventions play a critical role for transgender individuals. Pharmacists can help tailor GAHT regimens to individual patient needs, promoting safety and helping patients achieve their goals towards gender affirmation. Pharmacists and pharmacy technicians can create a more inclusive and safer environment when interacting with patients. As healthcare workers in the pharmacy setting, we can provide patients with the resources they need without judgement.

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INTRODUCTION

Gene therapy is a medical approach to replace missing genes or correct dysfunctional genes in patients with genetic diseases. Gene therapies are best suited for patients who have well-defined, single (monogenic) mutations.^1,2 Many are rare diseases for which there are few, if any, treatment options. Therapeutics to correct gene mutations are biologics with the potential to cure a variety of previously incurable diseases such as muscular dystrophy, hemophilia, cystic fibrosis, and some types of blindness. Scientists are also developing gene therapies to stop cancer-causing genes and boost immune responses against tumors.

The term “gene therapy” encompasses multiple broad strategies that can be separated into two general approaches: in vivo (performed inside an organism) and ex vivo (cells that are removed from the organism, genetically modified, and then returned to organism).³ Within these approaches, multiple techniques and delivery systems are currently used or in development:^4,5

• Viral vectors (in vivo or ex vivo)
• Non-viral delivery particles (in vivo or ex vivo)
• Gene editing (in vivo or ex vivo)
• Cell engineering (ex vivo only)

The entire field of gene therapy is beyond the scope of this activity. This activity’s focus will be in vivo gene delivery via engineered adeno-associated virus (AAV), with some discussion of gene therapy’s basics and background. This is valuable information for pharmacists and pharmacy technicians as this complex biologic class matures and more gene therapies become available to patients.

BASICS OF GENE THERAPY

Gene Therapy Terminology

People outside of the field may be unfamiliar with many terms used to describe gene therapies. Table 1 defines common terms.

Table 1. Common Terms Used to Describe Gene Therapy^6,7,8

DNA, deoxyribonucleic acid.

We have used brand drug names preferentially throughout this activity because generic names for gene therapies are complex (See Sidebar).

SIDEBAR: What’s in a Name? How Are Gene Therapies Named?^9,10

For in vivo gene therapies, the generic names are composed of two words:

• First word corresponds to the gene component
  • Prefix: random element to provide unique identification
  • Infix: element to denote the gene’s pharmacologic class (gene’s mechanism of action)
  • Suffix: element to indicate “gene”
• Second word corresponds to the vector component
  • Prefix: random element to provide unique identification
  • Infix: element to denote the viral vector family
  • Suffix: element to identify the vector type (non-replicating, replicating, plasmid)
  • 4-letter distinguishing suffix: devoid of meaning and attached to the core name with a hyphen

Example:

The Pros and Cons of Gene Therapy 

Patients and/or caregivers considering gene therapy should consider several factors^11-13:

• Duration of efficacy
  • PRO: Potential exists for permanent correction of a disease state. If successful, patients may not need lifelong treatments/medications.
  • CON: Gene therapy is relatively new and long-term efficacy data is lacking. If gene expression wanes over time, patients may need redosing (which may be impossible) or alternative treatments.
• Safety
  • PRO: Regulatory agencies have approved several products, and safety data is available.
  • CON: Complete understanding of adverse effect mechanisms is lacking, and long-term safety information doesn’t exist.
• Cost
  • PRO: A curative gene therapy may be more cost-effective than a lifetime of other medications/treatments.
  • CON: Available gene therapies are very expensive, $2.9 to $3.5 million for the AAV in vivo therapies approved in 2022 and 2023.

The History of Gene Therapy

Gene therapy is a relatively new field. Clinicians ran the first clinical trial in 1990. Scientists made several advancements in the 1990s and early 2000s, and progress has rapidly accelerated since then.¹⁴ (See Sidebar).

ABBREVIATIONS: AAV, adeno-associated virus vector; Ad, adenovirus; ADD, adenosine deaminase deficient; ALL, acute lymphoblastic leukemia; CALD, cerebral adrenoleukodystrophy; CAR T, chimeric antigen receptor; Cas9, CRISPR-associated protein 9; CRISPR, clustered regularly interspaced palindromic repeats; DMD, Duchenne muscular dystrophy; EMA, European Medicines Agency; FDA, Food and Drug Administration; HSC, human stem cells; LV, lentivirus; DLBCL, diffuse large B-cell lymphoma; SCD, sickle cell disease; SCID, severe combined immunodeficiency disorder; SMA, spinal muscular atrophy; TDT, transfusion-dependent thalassemia.

Gene Therapy Systems

Viral Vectors

Prototypical gene therapy is an in vivo approach to curing genetic diseases. It uses a delivery vehicle, such as an engineered virus that encapsulates the gene of interest (GOI) for injection into a patient by various routes, such as intravenous (IV), intraocular, or intrathecal.³⁹ This method takes advantage of a virus’s natural ability to enter mammalian cells efficiently. Once the delivery vehicle enters host cells, the encapsulated gene drives production of the missing or faulty protein. Clinicians use this approach for diseases such as muscular dystrophies, where mutations in the dystrophin gene cause progressive weakness and muscle-wasting, and cystic fibrosis, where mutations in the cystic fibrosis transmembrane conductance regulator gene impair lung function.

Non-viral Delivery Vehicles

Non-viral delivery vehicles, such as nanoparticles, can also deliver genes or gene editing systems in vivo. These particles use biocompatible materials such as polymers and lipids to carry genes or nucleic acids into cells.³ Researchers can customize a particle’s physiochemical properties to target the intended cell types better and evade immune responses. Non-viral particles are less efficient than viruses at entering cells but may have several other advantages. It’s likely that most patients are immunologically naïve to manufactured particles and lack pre-existing antibodies that may prevent successful uptake by cells. Non-viral particles may also be easier to manufacture and purify, making them more cost-effective to produce than viral vectors.⁴⁰

Recent gene therapy clinical trials using nanoparticles or lipid nanoparticles include the following^41-43:

• Reqorsa: contains a tumor suppressor gene encapsulated in a lipid nanoparticle for treatment of several types of lung cancer
• NTLA-2001: contains a gene editing system encapsulated in a lipid nanoparticle for treatment of hereditary transthyretin amyloidosis (a disease which deposits abnormal protein [amyloid] in organs)

Gene Editing Systems

Gene editing systems, which can be in vivo or ex vivo approaches, can provide precise, targeted gene modifications. Gene editors are engineered nucleases (enzymes) that produce double-stranded breaks at a specific target site. These breaks stimulate the cell’s natural DNA repair mechanisms, resulting in the repair of the break by homology-directed repair or non-homologous end joining. With these systems, target-specific DNA insertions, deletions, modifications, or replacements are all possible.^3,44

Many gene editing tools exist, including^3,44

• clustered regularly interspaced short palindromic repeats (CRISPR) Cas-associated nucleases
• transcription activator-like effector nucleases (TALENs)
• zinc-finger nucleases (ZFNs)
• meganucleases (MNs)

Gene editing ex vivo systems are a fast-growing area with many programs in development.⁴¹ In vivo gene editing is rife with challenges, especially those concerning delivery to the intended cells. Gene editing systems are an evolving cutting-edge platform reviewed in much more detail elsewhere.^3,44,45

Ex Vivo Gene Therapy

In ex vivo gene therapy, medical and/or laboratory personnel remove a patient’s cells from the body, genetically modify them (using viral vectors, non-viral delivery particles, or gene editing systems), and then re-introduce them into the patient. Alternatives to the use of a patient’s cells include genetically modified cell lines or cells from another donor. The use of autologous (patients’ own) cells avoids the need to find an immuno-compatible donor. Examples of systems include chimeric antigen receptor (CAR) T cells and engineered hematopoietic stem cells (HSC). CAR T cells are T lymphocytes that are modified to recognize tumor antigens, such as the B lymphocyte antigen Cluster of Differentiation-19 (CD-19) and B-cell maturation antigen (BCMA). Once genetically modified, the CAR T cells bind to cells expressing the tumor antigen and subsequently kill them. HSC have the ability for self-renewal and to differentiate into multiple cell lineages, therefore engineering them to correct genetic flaws such as enzyme deficiencies and hemoglobinopathies (inherited disorders affecting hemoglobin, the molecule that transports oxygen in the blood) makes them a promising approach.

Several products have received regulatory approval in the United States (U.S.)⁴⁶:

• Autologous CAR T cells^47-50
  • CD19-directed autologous T cell immunotherapies for the treatment of various types of B cell lymphomas include the following:
    • Yescarta (axicabtagene ciloleucel) – approved 2017
    • Kymriah (tisagenlecleucel) – approved 2017
    • Tecartus (brexucabtagene autoleucel) – approved 2020
    • Breyanzi (lisocabtagene maraleucel) – approved 2021
  • BCMA-directed autologous T cell immunotherapies for treatment of relapsed or refractory multiple myeloma include the following^51,52:
    • Abecma (idecabtagene vicleucel) – approved 2021
    • Carvykti (ciltacabtagene autoleucel) – approved 2022
• Autologous HSC-based gene therapies include the following^53-56:
  • Skysona (elivaldogene autotemcel) – slows neurological dysfunction in cerebral adrenoleukodystrophy by inducing synthesis of adrenoleukodystrophy protein – approved 2022
  • Zynteglo (betibeglogene autotemcel) – corrects β-thalassemia by adding functional copies of a modified β-globin gene into the patient’s HSC – approved 2022
  • Casgevy (exagamglogene autotemcel) – first FDA-approved CRISPR/Cas9 gene-editing therapeutic; corrects sickle cell disease (SCD) and transfusion-dependent β-thalassemia by adding functional copies of a modified β-globin gene into the patient’s HSC – approved 2023
  • Lyfgenia (lovotibeglogene autotemcel) – corrects SCD by adding functional copies of a modified β-globin gene into the patient’s HSC – approved 2023

CAR T cell gene therapy is an effective treatment for several types of cancers but comes with many challenges to patients, medical professionals, and pharmacy personnel. Product manufacturing, administration, and adverse effect mitigation are more complex than for many other treatment types. Medical, laboratory, and/or pharmacy personal carry out the following key steps at specialized medical centers^47-50:

1. Collect the patient’s white blood cells (leukapheresis)
2. Manufacture the CAR T cells in a laboratory with a typical time frame of two to four weeks
   • Patients may need to travel to and remain near the center while they wait for the cells
   • If the process fails, then personnel must repeat the cell collection and CAR T cell manufacturing
3. Administer chemotherapy to deplete the patient’s lymphocytes, two to 14 days prior to CAR T cell infusion, which makes room for the CAR T cells
4. Administer the CAR T cells to the patient by slow infusion to minimize infusion-related adverse reactions
5. Monitor the patient for at least four weeks, likely requiring the patient to stay at or near the treatment center

This therapy class carries Boxed Warnings:

• CD-19 directed therapies^47-50,57
  • Cytokine release syndrome (CRS): over-activation of the immune system with release of large amounts of cytokines (immune system proteins); this is a common, potentially life-threatening adverse event
  • Neurotoxicity: the mechanism by which this occurs is not well understood, but it is common and can be life-threatening

• BCMA-directed therapies^53,54
  • CRS and neurotoxicity as listed for CD-19 directed therapies
  • Hemophagocytic lymphohistiocytosis/macrophage activation syndrome: a hyperinflammatory immune response that can be life-threatening
  • Prolonged cytopenia (low numbers of blood cells) with bleeding and infection; can be life-threatening

Ex vivo gene therapy with autologous HSC is also a complex process with multiple challenges and toxicities.^53,54 For these therapies, medical personnel pretreat patients with granulocyte-colony stimulating factor to increase production and release of HSCs from bone marrow. Laboratory staff then collect and purify HSC from the patient’s blood. Staff may need to collect cells more than once to amass the required number of cells or in cases where manufacturing fails. Laboratory staff genetically modify the patient’s HSCs, typically with a lentiviral vector, to express the GOI. The cell manufacturing process can take up to three months. The modified cells require cryopreservation and liquid nitrogen storage conditions, adding to the process’s complexity.

When the cells are ready, medical personnel administer lymphocyte-depleting chemotherapy to the patient to remove HSCs that are making the faulty protein and to make room in the bone marrow for the genetically modified HSCs. Next, medical personnel infuse the thawed HSCs to the patient intravenously. After infusion, patients may need to stay at the medical center for several months for recovery and monitoring.

The prescribing information lists toxicities including prolonged cytopenias, serious infections, and an increased risk for lentiviral vector-mediated oncogenesis (development of a new cancer). It recommends patient monitoring for 15 years to life for hematologic malignancies. Skysona and Lyfgenia have Boxed Warnings for hematologic malignancy.^53,56

The overview above describes how the field of gene therapy is broad and encompasses multiple approaches. New and evolving approaches include non-viral delivery, gene editing, and ex vivo cell engineering; they have recently started to become available to patients. This is an exciting and hopeful time for patients with genetically-linked diseases, and it is likely that many more effective and approved therapies will be available soon.

AAV-BASED IN VIVO GENE THERAPY

Although researchers are developing viral vectors based on many types of viruses (e.g., adenovirus, gamma retrovirus, herpes simplex virus, lentivirus) adeno-associated virus (AAV) has emerged as the leading viral vector for in vivo gene therapy with five current regulatory approvals in the U.S. and many more programs under development.^41,46 Its favorable characteristics include not causing human disease, inability to replicate in the host without a helper virus, and ability to elicit a low host immune response relative to many other viruses. Since the expression cassette is typically maintained on an episome, scientists expect AAV-based vectors to have a low frequency of integration into the host genome, conferring a minimal risk of cancer.⁵⁸ In addition, at least one serotype of AAV (AAV9) can cross the blood-brain barrier making AAV a suitable choice for neurologic diseases without invasive local administration of the vectors into the brain. Researchers find AAV-based vectors to be attractive, versatile tools with suitable properties and utility for a wide variety of diseases.

AAV Biology

Naturally occurring AAVs are small, non-enveloped viruses that belong to the Parvovirus family. They have a linear single-stranded DNA genome of approximately 4.7 kilobases, including rep and cap genes that encode for replication and capsid proteins, respectively.³ Figure 1A illustrates the genomic structure of a wild type (naturally occurring) AAV.

In engineered AAVs used for gene therapy, developers remove the rep and cap genes and replace them with an expression cassette, as illustrated in Figure 1B. The expression cassette contains the GOI, regulatory elements (promoter/enhancer), and poly-adenosine tail (to stabilize the messenger RNA and facilitate translation into protein) flanked by inverted terminal repeats (ITRs; required for genome replication and packaging). The expression cassette replaces approximately 96% of the native genome.³

Figure 1. Genomic Structure of Wild Type AAV and Engineered AAV Vector

cap, capsid gene; GOI, gene of interest; ITR, inverted terminal repeat; rep, replicase gene.

AAV capsids in both the wild type AAV and engineered AAV vectors are composed of three viral proteins (VPs) named VP1, VP2, and VP3. Sixty molecules of these proteins, estimated to exist in a 1:1:10 ratio (VP1:VP2:VP3), assemble into each icosahedral capsid (Figure 2). The VP sequences overlap, with VP1 being 137 amino acids longer than VP2, which is 57 amino acids longer than VP3. Differences in VP3 sequences distinguish one AAV serotype from another.⁵⁹

Figure 2. Protein Structure of the AAV Capsid

VP, viral protein.

AAV exists as at least 11 natural serotypes, which share about 51% to 99% sequence identity in their VP3 protein.^60,61 Sequence comparisons between different AAV serotypes identified nine variable regions situated on the capsid surface. The specific amino acid sequences of these regions impact AAV binding to host cell receptors, thus determining cell- and tissue-specific tropism (affinity for a specific tissue or cell type). These variable sequences also function as binding sites (epitopes) for AAV-specific antibodies, thus influencing host immune responses.⁶²

An AAV serotype can be tropic to multiple cell types and tissues, and multiple serotypes can be tropic to the same cells/tissues. Researchers isolate serotypes from non-human primates and develop synthetic serotypes using protein engineering to alter tropisms and/or evade pre-existing AAV-specific antibodies.¹

PAUSE AND PONDER: If your child had a life-shortening genetic disorder and a new AAV9-based therapy became available, how would you feel if your child had a high anti-AAV9 neutralizing antibody titer that excluded them from clinical trials or treatment?

Neutralizing antibodies (NAbs) are naturally occurring antibodies that bind to AAV surface epitopes and block uptake into target cells. NAb binding to the AAV capsid can induce rapid clearance of the gene therapy by the patient’s immune system. Clinical personnel must screen patients for pre-existing Nabs. Trial protocols and prescribing instructions often exclude patients with NAbs specific for the gene therapy’s serotype.

Older children and adults tend to have a high prevalence of pre-existing antibodies against commonly circulating (wild type) AAV serotypes because of previous exposure to these viruses over the course of their lives. For example, studies showed that approximately 40% of humans have NAbs to AAV serotypes 5, 6, 7, 8, and 9.⁶³ Between 6% and 95% of individuals with hemophilia A and B have AAV-specific antibodies based on AAV serotype and assay used.⁶⁴ In addition, due to the high degree of conservation of capsid protein amino acid sequences, pre-existing antibodies to one serotype may cross-react with other serotypes, further limiting the availability of a therapy for a patient. Patients without NAbs prior to gene therapy will develop high titers of NAbs following vector administration, rendering them ineligible for additional rounds of gene therapy with the same vector or a cross-reactive serotype.^1,63-65

Vector Design

To create a vector for a particular disease, drug developers try to target an AAV vector to the specific cell or tissue type where gene correction is needed. The capsid serotype choice significantly influences this decision.

AAV2, AAV5, AAV6, AAV8, and AAV9 account for a majority of the ongoing AAV gene therapy clinical trials.^60,66 Commonly, AAV2 or AAV8 is the choice for ocular therapies; AAV2, AAV8, AAV5, and AAV9 are best for liver targeting; and AAV2 and AAV9 are preferred targeting muscle or the central nervous system. Some researchers are also using AAV serotypes isolated from rhesus monkeys, such as rh74.^60,67 As discussed, AAV9 can cross the blood-brain barrier, allowing IV administration of this serotype to target brain tissue while avoiding invasive intrathecal injections.^60,68 Therefore, AAV9 is a popular vector to treat many diseases affecting the nervous system.

Developers derive the capsids of AAV vectors either from natural AAV viruses or by engineering capsids through rational design, directed evolution, or computer-guided strategies. The impetus to develop AAV vectors with capsids from less common AAV serotypes or novel engineered AAV capsids serves to improve or modify tissue targeting and circumvent immune recognition.⁶⁹

Considerations for vector design include^61,62

• Choosing the best AAV serotype to target the intended cell type or tissue, using the desired route of administration
• Potential for tissue-specific promoters (e.g., targeting the muscle for muscular dystrophy or the liver for hemophilia) rather than constitutive promoters (that will drive gene expression in a wide range of tissues and perhaps result in off-target toxicity)
• Whether an enhancer is needed to boost expression in the target tissue to achieve desired therapeutic effect
• Modifying capsid epitopes to reduce recognition/response from the host immune system

Vector Production and Purification

Once developers choose the best capsid serotype and design the vector, they proceed to the manufacturing step. Gene therapies are complex biologics, and manufacturing and purification are of utmost importance for efficacy, safety, and product stability. Regulatory agencies require good manufacturing practice compliance.⁷⁰

Scientists commonly use mammalian cell lines to propagate engineered AAV vectors and then purify the vectors from cell lysates. Rigorous purification is essential. As the science of gene therapy matures, drug developers continuously improve purification methods. Contaminants from the engineered AAV cultivation process are a potential source of toxicity and can induce unwanted immune responses. Release testing of the final product in the U.S. must comply with a series of FDA-established requirements and predetermined specifications to determine product safety, purity, concentration, identity, potency, and stability.⁷¹ Characterization of the final product includes a determination of the viral genome (vg) titer, infectious titer (potency), product identity (AAV capsid and genome), and therapeutic gene identity (expression/activity).⁷²

Gene therapy developers follow these steps to manufacture AAV-based therapies^73-75:

1. Use conventional recombinant DNA technology in bacterial systems to produce the plasmids
2. Use mammalian cell lines, such as human embryonic kidney 293 cells, or insect cell lines, such as the baculovirus/insect cell system, to produce the vectors
3. Transfect (introduce genetic material into a cell) three plasmids into the cell line
   • a recombinant AAV plasmid containing the expression cassette (see Figure 1b)
   • an adenovirus-based helper plasmid supplying genes needed for virus replication
   • a plasmid containing the essential rep and cap genes needed for virus replication and capsid formation
4. Collect produced vectors from the cells and purify them. Complex purification processes require multiple methods that may be specific for each individual contaminant. Rigorous purification minimizes patient risk (see Sidebar). Examples of purification process steps (and techniques used) include the following:
   • Cells lysis to release the viral particles (detergent, mechanical stress, hypertonic shock, freeze-thawing)
   • Removal of nucleic acids (nuclease treatment), cell fragments and proteins, cell culture contaminants (centrifugation, filtration, chromatography)
   • Separation of full vector particles from empty particles (cesium chloride gradient ultracentrifugation or chromatography)
5. Formulate vectors after purification for administration to the patient. Formulation optimization prior to manufacture is not trivial. Some considerations are:^73-75
   • Formulation chemical composition must be optimized for intended route of administration
   • Formulation must be sterile and have low endotoxin concentration
   • Formulation must minimize product degradation to avoid aggregation and loss of efficacy due to product instability

SIDEBAR: Patient Safety: The Importance of Purification of AAV^69,74

• Non-vector sequences (including plasmid DNA, helper virus DNA, and DNA from the cell line used to produce the vector) can unintentionally be packaged into the capsids. AAV vector genomes can recombine with non-vector DNA, resulting in AAV vectors that contain chimeric (mixtures of DNA from different sources) sequences. The behavior of these unintended sequences is unpredictable in patients.
• Capsids containing the complete intended therapeutic gene, partial sequences, unintended chimeric sequences, or no genetic sequence material at all (empty capsids) are all possible outcomes of vector manufacturing. Administering a mixture of different forms of the therapeutic to patients may result in a partial effective dose, thus lowering potency and necessitating administration of higher overall numbers of AAV particles to achieve efficacy. The higher the number of AAV particles, the higher the risk of toxicities and immune system activation.

Toxicities/Adverse Events

Although AAV gene therapy is generally considered safe, multiple treatment-emergent serious adverse events have occurred following gene therapy administration to patients. These include severe hepatoxicity and thrombotic microangiopathy (TMA). Other potential toxicities and identified risks include myocarditis, neurotoxicity (dorsal root ganglion [DRG] degeneration), oncogenicity, and immunotoxicity.⁶⁹

In general, AAV vectors administered IV first travel to the liver. Liver enzyme increases denoting liver damage commonly occur and corticosteroid treatment is often effective. On occasion, acute serious liver injury, liver failure, and death have occurred. Although the mechanism is not completely understood, more severe liver injury appears to correlate with higher vector doses. Severe liver injury following AAV vector administration for spinal muscular atrophy (SMA) and X-linked myotubular myopathy genetic diseases has occurred.^69,76

TMA is a pathological condition characterized by formation of thrombi (clots) in small blood vessels, following endothelial cell injury. TMA’s clinical presentation often includes complement activation, cytokine release, thrombocytopenia (decreased platelets), and kidney injury/failure. Several cases of TMA have been reported in patients or clinical trial participants following AAV gene therapy for SMA and Duchenne muscular dystrophy (DMD). Treatments for affected patients included hemodialysis, platelet transfusion, and the complement inhibitor eculizumab. As with severe liver injury, TMA development appears to be related to high vector doses.^77,78

Several patients in DMD clinical trials have developed myocarditis, which was fatal in one patient. A hypothesis is that pre-existing inflammation in DMD patients’ muscles, including heart muscle, worsened upon local expression of dystrophin. Steroid treatment successfully resolved myocarditis in some cases.⁷⁹

DRG degeneration/toxicity is an identified potential risk of AAV gene therapy. DRGs are collections of sensory neurons that relay impulses from the periphery to the central nervous system. Researchers have observed AAV vector-induced DRG toxicity mainly in non-clinical studies with pigs and non-human primates. Direct administration of AAV into cerebral spinal fluid and high vector doses were contributing factors. Pathology studies have detected DRG degeneration in autopsy samples from humans who received AAV gene therapy. Scientists do not completely understand DRG toxicity’s underlying mechanisms in animals or the significance of clinical translation to humans.⁸⁰

Oncogenicity due to insertional mutagenesis (introducing foreign DNA into a person’s genome) is a potential risk of gene therapy. Studies in mice that received AAV vectors revealed integration events and hepatocellular carcinoma. Hepatocyte clonal expansion occurred in dogs following AAV vector administration although tumors were not found. AAV vector genome integration into chromosomes has been detected in humans, but so far AAV-associated oncogenesis has not been reported.⁵⁸ Due to the potential risk, regulators expect long-term monitoring after vector administration.^69,81

Although immune responses to wild type AAV are low relative to other viruses, AAV can engage all arms of the immune system and can do so robustly especially when high vector doses are administered. The immune response to AAV gene therapy is complex, and poorly understood, and can contribute to loss of efficacy and adverse effects. Local (rather than systemic) dosing, use of tissue specific promoters, and increasing the vector’s potency (increasing promoter strength/achieving higher levels of expression per AAV particle) may effectively minimize toxicity.^65,76,82,83

Immune responses to AAV gene therapy include the following^65,66,79,82:

• Innate immune responses: may lead to cytokine induction and/or activation of the complement cascade (e.g., toll-like receptor recognition and signaling in response to capsid proteins and nucleic acids)
• Humoral responses: antibody binding to AAV capsid may activate complement and immune cells and remove the vector from circulation before it can reach its target tissue. After gene therapy administration, the body generates new antibodies that can be specific for a capsid or transgene product.
• Cellular immune responses: may lead to inflammation and elimination of the cells producing the disease-correcting protein (e.g., activation/expansion of capsid- or transgene-product-specific cytotoxic T lymphocytes)

APPROVED IN VIVO GENE THERAPIES

As of December, 2023, the FDA approved eight in vivo gene therapies, five of which are AAV based.⁴⁶

Non-AAV-Based Therapies

Three of the FDA-approved in vivo gene therapies are non-AAV based; they are adenovirus (Ad)-based or herpes simplex virus (HSV)-based. None are systemically administered, but instead are administered locally to the skin or bladder.

Vyjuvek (beremagene geperpavec-svdt) is a live, replication deficient HSV type 1 (HSV-1) vector genetically modified to express human type VII collagen. Vyjuvek is indicated for wound treatment in patients with dystrophic epidermolysis bullosa with mutation(s) in the collagen type VII alpha 1 chain gene. Topical application to wounds induces production of the mature form of type VII collagen leading to wound healing.⁸⁴

Adstiladrin (nadofaragene firadenovec-vncg) is a non-replicating adenoviral serotype 5 vector genetically modified to produce human interferon α-2b (IFNα-2b). Adstiladrin is indicated for patients with high-risk Bacillus Calmette-Guérin-unresponsive non-muscle invasive bladder cancer with carcinoma in situ with or without papillary tumors. Intravesical (within the bladder) instillation results in local expression of IFNα-2b protein that is anticipated to have anti-tumor effects.⁸⁵

Imlygic (talimogene laherparepvec) is a live, attenuated HSV vector genetically modified to replicate within tumors and to produce the immune stimulatory protein granulocyte-macrophage colony-stimulating factor (GM-CSF). Imylgic is indicated for local treatment, by intralesional injection of unresectable cutaneous, subcutaneous, and nodal lesions in patients with melanoma recurrent after initial surgery. Imylgic causes tumor lysis followed by release of tumor-derived antigens, which together with virally derived GM-CSF may promote an antitumor immune response. However, the exact mechanism of action is unknown.⁸⁶

AAV-Based Therapies

Luxturna (voretigene neparvovec-rzyl) is a genetically modified non-replicating AAV2 expressing the human retinoid isomerohydrolase (RPE65) gene approved in 2017. It’s used to treat patients with confirmed biallelic RPE65 mutation-associated retinal dystrophy, a condition causing progressive retinal degeneration and dysfunction, which can lead to vision loss and blindness over time. Retinal pigment epithelial (RPE) cells produce RPE65. Mutations in this gene result in vision impairment, so Luxturna aims to correct these mutations. A clinician administers 1.5 x 10¹¹ vg of Luxturna subretinally (directly into the space beneath the retina) to each eye on separate days, at least six days apart. Patients typically take systemic oral corticosteroids starting three days before its administration and continuing with a tapering dose for 10 days. Preparation of Luxturna for administration is complex and includes thawing, dilution, and preparation of syringes for injection. Warnings and precautions include endophthalmitis (infection/inflammation of the inner structures of the eye), permanent decline in visual acuity, retinal abnormalities, increased ocular pressure, intraocular air bubble expansion, and cataracts. Immune responses to Luxturna were mild in clinical trials, perhaps due to corticosteroid administration.²³

Zolgensma (onasemnogene abeparvovec-xioi) is a genetically modified non-replicating AAV9 expressing the human survival motor neuron (SMN) protein. The FDA approved it in 2019 for treatment of patients younger than 2 years of age with spinal muscular atrophy (SMA) with bi-allelic mutations in the SMN1 gene. SMN protein is key for muscle development and movement and Zolgensma aims to correct these mutations to treat the disease. After Zolgensma is thawed, a clinician administers 1.1 × 10¹⁴ vg/kg of Zolgensma intravenously by slow infusion. Patients typically take systemic corticosteroids starting one day before Zolgensma administration and continuing for a total of 30 days. Serious adverse effects described in the Boxed Warning include acute liver injury and failure with fatal outcomes. Other warnings and precautions include systemic immune response, thrombocytopenia, TMA, and elevated troponin (a protein involved in muscle contraction).⁸⁷

Hemgenix (etranacogene dezaparvovec-drlb) is a genetically modified non-replicating AAV5 expressing human coagulation Factor IX (Padua variant), under control of a liver-specific promoter. Approved in 2022, it is employed to treat male patients with hemophilia B (congenital Factor IX deficiency). The Padua variant has an 8-fold higher specific activity relative to wild type Factor IX, and Hemgenix would ideally correct the disease by providing circulating Factor IX activity. Clinicians administer 2.0 × 10¹³ gc/kg of Hemgenix by slow intravenous infusion. Hemgenix is a refrigerated suspension that requires dilution into normal saline. The prescribing information recommends corticosteroids, not prophylactically, but only if the liver enzyme aspartate aminotransferase (AST) increases to twice the patient’s baseline value. Warnings and precautions include infusion reactions (including anaphylaxis), hepatotoxicity, and hepatocellular carcinogenicity (theoretical risk if vector DNA integrates into the host cell genome).⁸⁸

Elevidys (delandistrogene moxeparvovec-rokl) is a genetically modified non-replicating AAVrh74 (originally isolated from rhesus monkeys) expressing human micro-dystrophin. The FDA approved it in 2023 for treatment of ambulatory 4- to 5-year-old patients with DMD with a confirmed mutation in the dystrophin gene. The vector’s promoter/enhancer drives transgene expression predominantly in skeletal and cardiac muscle. The dystrophin protein’s micro version consists of selected domains of dystrophin that confer function to muscle cells. After Elevidys is thawed, clinicians administer 1.33 × 10¹⁴ vg/kg by intravenous infusion using a syringe infusion pump. The prescribing information recommends prophylactic corticosteroids following a complex administration and tapering schedule, which is further complicated in patients with DMD already on a corticosteroid regimen. Warnings and precautions include acute serious liver injury, immune-mediated myositis, and myocarditis.⁸⁹

Roctavian (valoctocogene roxaparvovec-rvox) is a genetically modified non-replicating AAV5 expressing the B-domain-deleted form of human coagulation Factor VIII (the smallest active form of Factor VIII) under control of a liver-specific promoter. Approved in 2023 for treatment of male patients with severe hemophilia A, clinicians administer Roctavian after thawing at 6.0 × 10¹³ vg/kg by intravenous infusion using a syringe infusion pump. The prescribing information recommends corticosteroids, not prophylactically, but only if liver enzymes increase to 1.5 times the patient’s baseline or to above the upper limit of normal. Warnings and precautions include infusion reactions (including anaphylaxis), hepatotoxicity, and thromboembolic events.⁹⁰

PAUSE AND PONDER: The prescribing information for Hemgenix and Roctavian do not recommend these gene therapies for women. Why?

A LOOK TO THE FUTURE

As discussed above, the FDA has approved five AAV-based gene therapies, Figure 3 illustrates disease indications being studied in AAV-based clinical trials including 90 ongoing, interventional studies.⁴¹

Figure 3. AAV-based gene therapy clinical trials for different disease indications as a percentage of all AAV-based clinical trials for therapies not yet approved for marketing⁴¹

The percentages of each disease indication were calculated based on the total of current AAV-based interventional clinical trials. Clinical trials were identified using the search terms gene therapy and adeno-associated (for condition/disease) and interventional (study type). Trials designated as recruiting, active – not yet recruiting, enrolling by invitation, and completed were included in the analysis (n = 73). Trials designated as terminated, suspended, or unknown status were not included. Data are current as of April 12, 2024.

Ophthalmology and neurology represent the highest percentage of forthcoming therapies. Within the ophthalmology category, multiple trials are underway for achromatopsia (color blindness), amaurosis (complete vision loss without visible eye damage; typically, an optic nerve disease), and retinitis pigmentosa (progressive vision loss due to retina deterioration), among others. The neurological disease category includes trials for Alzheimer’s disease, Huntington’s disease, Parkinson’s disease, and others. Hematological and musculoskeletal clinical trials are highly focused on hemophilia and muscular dystrophies, respectively. The metabolic disease category is diverse containing a few trials each for numerous genetic diseases.⁴¹

Controlling the immune response to AAV vectors is one of the biggest hurdles for future therapeutics. The human immune system is complex and very efficient. Often, it has a back-up plan in case an organism escapes the first round of attack and usually a back-up plan for the back-up plan. It becomes impossible for an AAV vector (a virus in sheep’s clothing) to go unnoticed, especially when the doses are greater than 1 trillion vg/kg of body weight. Thus, a patient’s immune system will go into action starting shortly after receiving gene therapy and mount a multi-pronged attack.

New and improved strategies to control immune responses will greatly benefit patients. Researchers are diligently pursuing strategies (Table 2) that target the vector itself or immune system components.^91-93 Success will probably use a combinations of strategies.

Table 2. Strategies to Control or Circumvent Immune Responses^91-94

AAV, adeno-associated virus; IdeS, immunoglobulin G-degrading enzymes of Streptococcus pyogenes; IgG, immunoglobulin type G; NAb, neutralizing antibody.

Perfection of technologies to remove pre-existing NAbs would allow many more patients to be eligible for gene therapies. Curbing antibody production in the days following the gene therapy may boost efficacy, reduce toxicity, and allow patients to remain eligible for more than one round of AAV gene therapy if needed. Methods to control T cell-mediated responses would prevent destruction of the cells producing the transgene product, increasing the persistence of the curative gene expression.

Early clinical studies took a reactive approach to immune responses to AAV; they used medications such as corticosteroids following observation of increases in liver enzymes or signs of inflammation. More recently, efforts to identify drugs and combinations of drugs that will suppress the immune response prophylactically have accelerated^91,93:

• Corticosteroids (e.g., methylprednisolone): general anti-inflammatory
• Tacrolimus: inhibits T cell proliferation and differentiation
• Rituximab: depletes B cells to block antibody production
• Rapamycin (sirolimus): disrupts cytokine signaling resulting in inhibition of B cell and T cell activation
• Mycophenolate mofetil: inhibits B cell and T cell proliferation
• Eculizumab: complement inhibitor
• Hydroxychloroquine: inhibits toll-like receptor-9-mediated responses to viral DNA an antigen presentation

Researchers must investigate other key variables: the timing of immunosuppression initiation and the requisite treatment duration.

Many clinical trials have employed corticosteroids, but corticosteroids alone are insufficient to control immune responses. Regulators have approved the immunosuppressants listed above for indications other than gene therapy, and their safety profiles are known, making them logical choices to investigate for gene therapy indications. Future work must maximize safety and efficacy of AAV gene therapy while balancing adverse effects of the immunosuppressive regimens.⁹³

SUMMARY

Gene therapy is a relatively new, complex, and evolving field in medicine that offers hope to patients with previously incurable genetic diseases. The information presented here is intended to introduce a topic that pharmacists and pharmacy technicians may not have been previously exposed to, and perhaps inspire them to read more.

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