What is Amiodarone (antiarrhythmic medication) given for?

Amiodarone: Indications for Use

Amiodarone is primarily indicated for the secondary prevention of life-threatening ventricular arrhythmias, and is also commonly used as a second-line agent for atrial fibrillation in patients with structural heart disease. 1

Primary FDA-Approved Indications

• Amiodarone is FDA-approved for the secondary prevention of life-threatening ventricular arrhythmias, particularly in patients who have survived sustained ventricular tachyarrhythmias 1
• The North American Society for Pacing and Electrophysiology (NASPE) recommends amiodarone as the antiarrhythmic agent of choice in patients who have survived sustained ventricular tachyarrhythmias, particularly those with left ventricular dysfunction 1
• Intravenous amiodarone is indicated for emergency treatment of ventricular tachyarrhythmias with rapid onset of antiarrhythmic effect 1

Common Off-Label Uses

• Treatment of atrial fibrillation, although not FDA-approved for this indication 1
• Various practice guidelines recommend amiodarone as a second-line drug for long-term treatment of atrial fibrillation in patients with structural heart disease and in highly symptomatic patients without heart disease 1, 2
• Amiodarone may be used as an adjunct to reduce the frequency of ICD shocks in patients with implantable cardioverter-defibrillators 1
• Control of atrial fibrillation in selected highly symptomatic patients 1, 2

Electrophysiologic Effects

• Amiodarone is classified as a class III antiarrhythmic drug (Vaughan Williams classification), which indicates that it prolongs the QT interval 1, 3
• However, it has multiple additional effects: slows heart rate and atrioventricular nodal conduction (via calcium channel and beta-receptor blockade), prolongs refractoriness (via potassium and sodium channel blockade), and slows intracardiac conduction (via sodium channel blockade) 1, 3
• These combined effects make it effective against a wide variety of arrhythmias 4

Dosing Considerations

For Ventricular Arrhythmias:

• Oral loading: 800-1600 mg/day in divided doses until a total of 10g has been given, then maintenance of 200-400 mg/day 1, 2
• IV treatment for life-threatening arrhythmias: 150-mg IV bolus over 10 minutes (may be repeated in 10-30 minutes if necessary), followed by 1 mg/minute for 6 hours, then 0.5 mg/minute for 18 hours 1

For Atrial Fibrillation:

• Oral loading: 600-800 mg/day in divided doses until a total of 10g has been given, then maintenance of 200 mg/day 1, 2

Monitoring and Safety Considerations

• Amiodarone has numerous potential adverse effects requiring careful monitoring 1, 3
• Regular monitoring should include thyroid function tests, liver transaminase levels, and pulmonary function assessment every six months 1
• Close monitoring of prothrombin time and INR is essential when co-administered with warfarin, as amiodarone can increase warfarin effect 1, 3
• Digoxin levels should be monitored as amiodarone typically doubles serum digoxin concentration 1, 3
• Potential serious adverse effects include pulmonary toxicity, thyroid dysfunction, hepatotoxicity, and visual disturbances 3, 4

Clinical Efficacy

• Amiodarone has demonstrated high efficacy rates in controlling various arrhythmias 5, 4
• In early studies, total suppression and control was provided in 92.4% of patients with supraventricular arrhythmias and 82% of patients with ventricular arrhythmias 5
• It is considered the most effective antiarrhythmic drug available for maintaining sinus rhythm in patients with paroxysmal atrial fibrillation 4
• Amiodarone has been shown to reduce mortality in patients with congestive heart failure, with treatment reducing the annual mortality rate from 24.3% to 19.9% 1

Important Considerations and Pitfalls

• Despite its efficacy, amiodarone has a narrow therapeutic-toxic range requiring careful dosing 6
• The drug has an extremely long half-life (averaging 58 days), which can lead to delayed onset of both therapeutic and adverse effects 1, 7
• Amiodarone is a potent inhibitor of multiple cytochrome P450 enzymes, leading to numerous drug interactions 3, 7
• The maintenance dose should be kept at the lowest effective level to minimize adverse effects 1, 6