Amiodarone for Tachyarrhythmias: Pharmacology, Kinetics, and Efficacy

Amiodarone, although widely studied in Europe, is a recent addition to the investigational antiarrhythmics being used in the U.S. Pharmacologically, its primary cardiac effects are to increase coronary artery blood flow, increase the effective refractory period, and produce an atropine-resistant bradycardia. Amiodarone is incompletely (approximately 50 percent) and slowly (peak serum concentration approximately 6 h) absorbed. With chronic administration, it deposits both in adipose tissue and in organs with high blood perfusion. It has an apparent elimination half-life of 15-45 days, which presents unique dosing problems. The apparent therapeutic range is 0.6-3 microgram/ml. Amiodarone is 85-95 percent effective in the treatment of atrial tachyarrhythmias and 70-80 percent effective in ventricular tachyarrhythmias. It appears to be of particular value in chronic atrial fibrillation/flutter because it may be able to maintain sinus rhythm after cardioversion. Side effects, although uncommon, may prevent the drug from becoming a standard of therapy. Drug interactions, particularly with warfarin and digoxin, as well as pulmonary fibrosis are of concern.