24-hour antiarrhythmic effect of conventional and slow-release verapamil in chronic atrial fibrillation.

Twenty-four-hour heart rate control by verapamil given as conventional tablets t.d.s., or as a new slow release formulation once daily, has been compared in an open cross-over trial. Eight patients with chronic atrial fibrillation and one with chronic atrial flutter were studied outside hospital. Trough serum concentration of verapamil did not differ during the two dosage regimens (59 ng/ml - conventional formulation and 49.3 ng/ml - slow release tablet). The average serum concentration of digoxin in the patients was not changed. Compared to the control phase, both dosage regimens significantly and equally reduced individual and average heart rates throughout the entire 24-h period. A positive correlation between the serum concentration of verapamil and the relative increase in average R-R interval was demonstrated. It is concluded that dosage t.d.s. with conventional tablets of verapamil or once daily with the slow release formulation gave the same antiarrhythmic efficacy over 24 h, and was associated with equal trough serum concentrations of verapamil.