Effect of tocainide and quinidine on premature ventricular contractions.

The efficacy on premature ventricular contractions (PVCs) of tocainide 600 mg three times daily and of quinidine sulfate 300 mg four times daily administered for 8 wk versus placebo administered for 6 wk was determined in 41 patients. Neither the subjects nor the interpreter of the Holter recordings knew which medication had been used. Adverse effects occurred in 14 of 22 patients (64%) on tocainide and in nine of 19 (47%) on quinidine. Adverse effects caused 13 of 22 patients (59%) on tocainide and six of 19 (32%) on quinidine to discontinue medication. Reduction of PVCs greater than or equal to 75% over placebo occurred in one of nine patients (11%) on tocainide and in six of 13 (46%) on quinidine. By Lown's classification, a reduction in one grade of PVCs occured in two of nine patients (22%) on tocainide and in eight of 13 (62%) on quinidine. Neither tocainide nor quinidine has a high incidence of efficacy and a low incidence of adverse effects but, in the doses used, quinidine was more effective, benefited a larger proportion of patients, and induced fewer adverse effects than tocainide.