Objectives and Methods.—To gain insight into possible mechanisms of and predisposing
factors for torsades de pointes during terfenadine therapy, spontaneous reports in the US
Food and Drug Administration's Spontaneous Reporting System database were examined.
Based on the characteristics of the cases, in vitro cardiac electrophysiologic studies were
conducted to test the hypothesis that terfenadine, and not its major metabolite, has actions
similar to those of quinidine and is responsible for this form of cardiac toxicity. Design …