A multicenter, 2-week, double-blind, placebo-controlled, parallel group study was performed to determine the dose-response relation of
encainide administered 3 times daily and to determine its onset of action. To be included in the study, patients with benign or potentially lethal ventricular arrhythmias were required to have an average of at least 30
ventricular premature complexes (VPCs) per hour on 48-hour Holter monitoring after a 48-hour washout period without
antiarrhythmic drug treatment. Patients were randomly assigned to receive either placebo or 10, 25 or 50 mg of
encainide 3 times daily (tid) for 2 weeks. Of the 125 patients who entered the study, 122 were available for efficacy analysis. Efficacy was determined using 24-hour Holter monitoring on days 1, 7 and 14. There was no difference in frequency of VPCs or of
ventricular tachycardia events in the placebo and 10-mg-tid
encainide arms. At doses of 25 and 50 mg of tid,
encainide was effective in suppressing VPCs and in reducing the number of episodes of
ventricular tachycardia. A positive dose-response relation was identified. The onset of effect of
encainide was apparent at 3 hours and lasted for 24 hours with tid dosing. No difference in on-
therapy conditions were found among the 4 study arms. No patients were discontinued from the study because of electrocardiographic changes. There was no statistically significant change in vital signs or physical examination data. In 1 patient an elevated serum
glucose level developed. No symptomatic proarrhythmic events occurred and none required discontinuation of study medication.(ABSTRACT TRUNCATED AT 250 WORDS)