Flecainide dose-response relations in stable ventricular arrhythmias.

Flecainide acetate was evaluated in a placebo-controlled, dose-ranging study performed in patients with stable, high-frequency ventricular arrhythmias. Three centers studied 35 patients in a 3-stage protocol. After a placebo baseline, increasing oral dosages from 100 to 300 mg twice daily were evaluated. Placebo was then reinstituted and after arrhythmia had recurred, the patients were discharged on the effective dosage to return to the clinic for evaluation 7 and 14 days later. Thirty of 35 patients had more than 80% suppression (mean 96%) of ventricular premature complexes (VPCs) and more than 95% reduction in complex VPCs. Arrhythmia suppression was seen at dosages of 100 to 200 mg twice daily in 73% of the patients. Twenty-three percent of patients required 500 to 600 mg/day. Mild side effects were seen in 46% of patients. These resolved or became tolerable at lower dosages in most patients. Effective therapy continued for 2 years in 24 of 29 patients, without any evidence of chronic toxicity. Pharmacokinetic studies indicate that many patients require 5 to 7 days of constant dosing before reaching steady state. Flecainide acetate is an effective antiarrhythmic with a narrow range of effective dosages.