Class IB antiarrhythmic drugs: tocainide, mexiletine, and moricizine.

Tocainide, mexiletine and moricizine belong to class IB of Vaughan Williams system of classification of antiarrhythmic drugs. Mexiletine and tocainide have little or no effect on Phase 0 of action potential and conduction velocity. Their principal effect is to shorten the action potential duration. Moricizine does not fit precisely into the Vaughan Williams system of classification, but has been categorized with class IB agents because in vitro its effects are similar to those of lidocaine. In this article, the pharmacokinetics, electrophysiologic effects, and clinical uses of these three agents are reviewed.