Mexiletine is a Class IB antiarrhythmic which has basic and clinical electrophysiologic properties similar to
lidocaine. Like other Class I antiarrhythmic agents,
mexiletine blocks the rapid inward
sodium current responsible for phase 0 of the action potential. It has been noted in the clinical electrophysiology laboratory to have minimal effect on sinus node function and AV nodal and His-Purkinje system conduction. Pharmacokinetic studies have shown that oral absorption is rapid with bioavailability of 80-90%.
Mexiletine is predominantly metabolized by the liver with elimination half-life of 9 to 12 hours. The antiarrhythmic effects of the primary
drug's metabolites remain to be defined. Hemodynamic studies have shown
mexiletine to have a lesser negative inotropic effect than
procainamide or
disopyramide. Although
mexiletine as a single agent successfully suppresses 60 to 80% of spontaneous ventricular arrhythmias, it has lower efficacy in suppression of induced ventricular arrhythmias. Multiple studies have shown that as monotherapy
mexiletine is effective in preventing the induction of
ventricular tachycardia in approximately 20% of patients. When used in combination with a Class IA
antiarrhythmic drug for suppression of induced ventricular arrhythmias, multiple investigators have reported greater efficacy. Neurological side effects (
tremor,
dizziness,
memory loss) occur in approximately 10% of patients while gastrointestinal side effects (
nausea,
anorexia, gastric irritation) occur in up to 40% of patients. Proarrhythmia or other serious toxicity from the
drug is uncommon.