Tocainide and Mexiletine

Because currently available antiarrhythmic agents frequently produce side effects and are only moderately effective, a number of new drugs are currently in the late stages of premarketing development and should be available to'the practicing physician within the next year or two. Among these agents are tocainide (released for marketing in November 1984) and mexiletine (soon to be released), both close structural analogues of lidocaine that can be used orally. In fact, the tocainide molecule emerged from a systematic search of lidocaine analogues that might be useful for oral therapy.1 Mexiletine was originally developed as an anticonvulsant and anorexiant, and when its close structural resemblance to lidocaine was noted, antiarrhythmic studies were performed that showed its activity.2In basic electrophysiologic terms, both agents produce local anesthetic (sodium-channel blocking) effects similar to those of lidocaine,3,4although subtle differences in the time course of the drug-sodium channel interaction have been reported.5Like lidocaine,