The use of intravenous amiodarone in the acute therapy of life-threatening tachyarrhythmias.

0 VER THE PAST several years oral amiodarone has been shown to be effective for a wide variety of supraventricular and ventricular arrhythmias.‘-” A unique aspect of amiodarone therapy is the long time required to reach maximum efficacy.‘6’* For example, Rakita and Sobol used continuous ambulatory electrocardiographic monitoring to compare several different oral regimens for amiodarone loading and found that between 9.5 to 16.9 days were required for control of ventricular ectopy.16 Kadish et al demonstrated that the electrophysiologic effects of amiodarone differed at two weeks and 3 months, implying that the maximum effects of amiodarone were not present after two weeks of oral therapy.‘* A prolonged time to maximum clinical efficacy may have important implications in certain groups of patients. The natural history of spontaneous arrhythmias is highly variable. Some patients may have infrequent episodes of arrhythmia and long arrhythmia-free intervals. In these patients, oral amiodarone may be an appropriate agent. In contrast, other patients may have frequent recurrences of life-threatening arrhythmias or incessant tachycardias unresponsive to direct countershock. In these patients, rapid antiarrhythmic efficacy is important, and therefore oral amiodarone by itself may not be adequate therapy. There is evidence that amiodarone administered intravenously (IV) may have a rapid onset of action. Thus, IV amiodarone may be potentially useful in the therapy of patients with frequent or incessant arrhythmias. In addition, there may be patients with severe systemic illnesses in whom IV therapy may be the only method available for delivering an antiarrhythmic agent. This article will review the mechanisms of action of IV amiodarone, its pharmacokinetics and pharmacodynamics, some general considerations in its use, and the published clinical experience concerning its efficacy in the treatment of arrhythmias.