Chronic mexiletine therapy for suppression of ventricular arrhythmias.

One hundred patients with a 70% or greater reduction of ventricular premature contractions (VPCs) from baseline during 12 weeks of mexiletine therapy were continued on treatment for an additional 9 months. Fifteen patients did not have follow-up examinations. The response of the remaining 85 patients during this extended period of open-label mexiletine administration is described. Holter recordings were scheduled at 3-month intervals during this period. At these examinations, between 69 and 80% of patients maintained the same 70% or greater level of VPC suppression observed at the start of the 9-month treatment period. Mean and median levels of VPCs/h at each examination were significantly reduced from premexiletine levels throughout the study (p less than 0.0001). Blood tests and electrocardiographic intervals did not vary. The most frequently used dosage of mexiletine during each 3-month treatment period was 600 mg/day (50.0-55.6% of patients). Side effects warranted discontinuation of therapy in 8% (8/97) of patients, while in 25% (22/85), clinical evaluation resulted in a change in dosage level. Within a setting similar to that of clinical practice, long-term mexiletine administration for non-life-threatening ventricular arrhythmias was effective and well tolerated.