Clinical pharmacology and antiarrhythmic efficacy of encainide in patients with chronic ventricular arrhythmias.

We determined the pharmacokinetics, efficacy and therapeutic plasma concentration of encainide, a new antiarrhythmic drug that affects His-Purkinje conduction but not ventricular refractoriness. Nine patients with frequent and complex premature ventricular complexes were studied in a 3-day double-blind protocol. Each day, each patient received 75 mg of i.v. or oral encainide or placebo. Frequent blood samples for encainide plasma concentration determination and continuous ambulatory ECGs were obtained. There was a marked intersubject variation in bioavailability (mean 42 +/- 24%, range 7.4-82%), clearance (13.2 +/- 5.6 ml/min/kg, range 3.75-22.1 ml/min/kg) and half-life (3.4 +/- 1.7 hours i.v., 2.5 +/- 0.8 hours oral). Eight of nine patients had more than 90% suppression of premature ventricular complexes for 3-36 hours. Minimal antiarrhythmic plasma concentration was higher (39 +/- 54 ng/ml, range 3.5-170 ng/ml) after i.v. dosing than after oral dosing (14 +/- 16 ng/ml, range 1.5-48 ng/ml), suggesting an...