amiodarone

Amiodarone is a potent antiarrhythmic medication used to treat a wide range of tachyarrhythmias. It is class III by the Vaughan-William classification but exhibits properties of all four classes because it blocks multiple ion channels and receptors. The primary effect is prolongation of the cardiac action potential by potassium channel blockade, with additional sodium and calcium channel– and beta-adrenergic–receptor effects. Amiodarone is highly lipophilic with a large volume of distribution and a long half-life (approximately 40–55 days; slower terminal phase). An active metabolite, N-desethylamiodarone, contributes to activity.

Indications: It is used for life-threatening ventricular arrhythmias such as ventricular fibrillation and pulseless ventricular tachycardia, and for recurrent or refractory ventricular tachycardia. It is also used in selected patients to maintain sinus rhythm in atrial fibrillation or flutter when other therapies are unsuitable or poorly tolerated.

Administration and dosing: For acute management, intravenous regimens commonly start with a 150 mg bolus over 10 minutes, then 1 mg/min for 6 hours, then 0.5 mg/min for 18 hours. Oral loading is often 800–1600 mg/day for 1–2 weeks, followed by maintenance of 200–400 mg daily; dosing is individualized to response and tolerance.

Adverse effects and monitoring: Amiodarone can cause pulmonary toxicity (including interstitial pneumonitis and fibrosis), hepatotoxicity, thyroid dysfunction (due to iodine content), corneal deposits and photosensitivity, skin discoloration, and bradyarrhythmias or other rhythm disturbances. It interacts with many drugs (notably warfarin and digoxin), requiring monitoring of drug levels and organ function. Baseline and periodic evaluation of liver function, thyroid function, chest symptoms, and vision should be performed; consider avoiding use in pregnancy unless clearly necessary.