Dosing recommendations for encainide

Abstract

The onset of antiarrhythmic action of encainide in patients with ventricular arrhythmias occurred within 3 hours after a single dose of 25 or 50 mg. No significant antiarrhythmic activity was noted after only 10 mg. After 14 days of daily dosing, both the 25- and 50-mg dose levels of encainide administered 3 times/day abolished or decreased ventricular arrhythmias in patients tested over a 24-hour period, whereas the 10-mg dose was ineffective. In 5 well-controlled studies involving 331 patients, encainide produced a dose-related decrease in the absolute number of ventricular arrhythmias as well as an increase in the percentage of responders (>75% decrease in ventricular arrhythmias). Doses of 75 mg/day were required to obtain at least a 50% reduction in ventricular arrhythmias or 50% of patients responding or both. Three-times-a-day dosing was as effective as 4-times-a-day dosing. Further, doses >200 mg/day gave little or no increase in incidence of efficacy. Important side effects were very low using doses of ≤150 mg/day and increased significantly at ≥150 mg/day. It is recommended that encainide be initiated at 25 mg 3 times/day for 4 to 7 days, then carefully titrated upward, as needed, to 35 and 50 mg 3 times/day, respectively, every 4 to 7 days. If needed, 50 mg 4 times/day is an appropriate next dosage. Rapid dose escalation or doses >200 mg are discouraged. Patients with severe life-threatening arrhythmias should receive encainide in a setting with cardiac monitoring and advanced life support systems.