Multicenter controlled observation of a low-dose regimen of amiodarone for treatment of severe ventricular arrhythmias. Collaborative Group for Amiodarone Evaluation.

The clinical efficacy of a low-dosage schedule of amiodarone was tested in 58 patients with severe ventricular arrhythmias refractory to other drug treatments. The initially chosen regimen of 400 mg was effective at the end of the first controlled trial period (after 4 weeks) in 73% of the patients. The responsiveness was maintained with the smaller dosage of 200 mg in 68% of this group. The response was reestablished also in the patients who became nonresponders during the low-dose regimen when they returned to the initial (400-mg) dosage. No relation was found between clinical response and blood levels of amiodarone and of its deethylated metabolite. Adverse effects more often associated with amiodarone therapy were rare. However, careful monitoring of thyroid function allowed the detection in 10% of the patients of biochemically and functionally documented, but clinically silent, cases of hypo- or hyperthyroidism.