Pharmacokinetics and electrocardiographic effects of a new controlled-release form of flecainide acetate: comparison with the standard form and influence of the CYP2D6 polymorphism.

Objectives: Our objectives were study the single- and repeated-dose pharmacokinetics and electrocardiographic effects (QRS duration) of a new controlled-release form of flecainide acetate compared with the immediate-release form and to examine the influence of CYP2D6 activity.
Methods: Twenty-four healthy subjects (6 men and 6 women at both dosages) received single and repeated doses of 100 or 200 mg immediate-release and controlled-release flecainide in a randomized crossover design. Electrocardiograms were recorded and flecainide plasma concentrations were measured before administration and up to 96 hours after administration.
Results: The controlled-release formulation had sustained-release properties, with a significantly lower maximum concentration (C(max)) and delayed time to reach C(max). Compared with the immediate-release formulation, the relative bioavailability of the controlled-release formulation at steady state was 0.85 +/- 0.17 and 0.89 +/- 0.17 for the 100-mg/day and 200-mg/day doses, respectively. Trough flecainide plasma concentration at steady state was bioequivalent for both formulations. Maximum and minimum QRS increases were not significantly different for either the immediate-release or the controlled-release form of flecainide after administration of both single and repeated doses. Mean QRS duration during a dosing interval at steady state correlated with mean plasma concentration for both forms (pooled data; P <.001). The 95% confidence interval for this regression was 26% narrower for the controlled-release form than for the immediate-release form. Flecainide-induced QRS prolongation and pharmacokinetics were not significantly influenced by CYP2D6 activity.
Conclusions: Flecainide-induced QRS prolongation did not differ between the new controlled-release form and the immediate-release form. Flecainide plasma concentrations associated with the new controlled-release form predicted QRS prolongation with less variability compared with the immediate-release form. The CYP2D6 polymorphism did not appear to influence flecainide disposition kinetics or electrocardiographic effects at steady state.