Moricizine: a new class I antiarrhythmic.

The chemistry, pharmacology, pharmacokinetics, clinical efficacy, adverse effects, and dosage of the Class I antiarrhythmic agent moricizine hydrochloride are reviewed. Moricizine is chemically similar to the phenothiazines but does not appear to block dopaminergic receptors. Its major electrophysiologic actions are a concentration-dependent decrease in maximum rate of phase 0 depolarization; increased rates of phase 2 and 3 repolarization, decreased action potential duration, and decreased effective refractory period. Moricizine causes a dose-related prolongation of the PR interval and of AV nodal, infranodal, and intraventricular conduction times but has little effect on ventricular repolarization. The antiarrhythmic and electrophysiologic effects are not correlated with plasma concentrations of the drug or its metabolites. Moricizine reduces the occurrence of ventricular premature contractions (VPCs), couplets, and nonsustained ventricular tachycardia. It appears to suppress symptomatic nonsustained ventricular tachycardia, sustained ventricular tachycardia, and ventricular fibrillation or flutter. Moricizine appears to be as effective as quinidine and more effective than disopyramide, propranolol, and imipramine but less effective than flecainide and encainide at reducing VPCs. Moricizine continues to be evaluated in the Cardiac Arrhythmia Suppression Trial, which was designed to assess the long-term benefit of arrhythmia suppression in patients with left ventricular dysfunction after myocardial infarction. Moricizine seems to be better tolerated than quinidine, disopyramide, and imipramine and to have less proarrhythmic potential than flecainide or encainide. Noncardiac adverse effects include dizziness, nausea, and headache. Cimetidine appears to decrease moricizine clearance, and decreased theophylline clearance has been reported in subjects given moricizine. The usual adult dosage of moricizine hydrochloride is 600-900 mg/day given in three divided doses; an every-12-hour regimen may be used in some patients. Because of the risk of proarrhythmic effects, indications are limited to treatment of documented life-threatening arrhythmias. Moricizine will compete with other agents as first-line therapy for life-threatening arrhythmias.