Practical follow-up guidelines for patients treated with amiodarone

Amiodarone is a new antiarrhythmic drug approved for therapy of life-threatening ventricular tachycardia and ventricular fibrillation refractory to previous antiarrhythmic therapy. The drug is poorly absorbed and avidly binds to all adipose tissue within the body. As a result of its unique pharmacologic properties, a 1-2 month period of loading with a high dose is required before therapeutic and steady state tissue concentrations are achieved. Therefore, there is a delay in the onset of antiarrhythmic effects of the drug and evaluation of efficacy using either noninvasive or invasive techniques should be performed 1-2 months after the initiation of therapy. It has been reported that suppression of runs of ventricular tachycardia (VT) documented on ambulatory monitor correlates with long-term efficacy. When invasive electrophysiologic (EP) studies are used, continued inducibility does not predict recurrence. Other important factors from the EP test include the rate of the induced VT and prolongation of the refractory period. Another problem related to amiodarone's pharmacologic properties is the occurrence of side effects which generally develop after weeks to months of drug therapy. Moreover, the incidence of toxicity increases over time. Although most side effects are unrelated to dose or blood level, it is possible that they correlate with the cumulative dose administered or total period of drug exposure. Amiodarone causes side effects which involve many organ systems. Most side effects are minor and cause no or only minor symptoms. Serious side effects, primarily cardiac, pulmonary, neurologic and thyroid, occur in about 18% of patients and often requires drug discontinuation. Therefore, use of amiodarone requires careful and continuous follow-up and monitoring for efficacy and toxicity.