N-acetylprocainamide kinetics during intravenous infusions and subsequent oral doses in patients with coronary artery disease and ventricular arrhythmias

Acecainide pharmacokinetics in normal subjects of known acetylator phenotype

The purpose of this study was to determine the pharmacokinetics of acecainide (formerly N-acetylprocainamide) in six normal subjects of known acetylator phenotype. Three subjects were fast acetylators and three slow acetylators by sulfapyridine phenotyping criteria. Each subject received a 20-min, 3 mg kg-1 intravenous acecainide infusion. Concentrations of acecainide, procainamide, and their deethylated metabolites were measured in serum and urine samples using HPLC. Acecainide renal clearance, nonrenal clearance, steady-state volume of distribution, and other pharmacokinetic parameters were estimated using standard approaches. Acecainide renal clearance and steady-state volume of distribution were (mean +/- SD) 13.6 +/- 1.581 h-1 and 135 +/- 20.31, respectively, and were not significantly different in fast and slow acetylators. Acecainide nonrenal clearance in the six subjects was 3.0 +/- 1.01 h-1; however, nonrenal clearance in slow acetylators was 1.8 times that in fast acetylators (3.9 vs 2.21 h-1, p = 0.012) with clear separation of the subjects into two groups when the data were grouped by acetylator phenotype. The nonrenal clearance of acecainide was inversely correlated with percentage sulfapyridine acetylation. Computer simulations were conducted to explore possible explanations for the observed difference in nonrenal clearance.

Pharmacokinetics of N-Acetylprocainamide

Shortly after Dreyfus and his colleagues demonstrated that procainamide was metabolized by acetylation to N-acetylprocainamide (NAPA), Drayer, Reidenberg and Sevy reported that NAPA had antiarrhythmic activity in an animal model. We confirmed these findings and found that plasma levels of NAPA were high enough to warrant consideration in managing patients requiring procainamide therapy. However, the actual impetus for developing NAPA as an antiarrhythmic drug in its own right was provided by the initial studies of NAPA pharmacokinetics in normal subjects. In these studies, we showed that NAPA has an elimination-phase half-life that is more than twice as long as procainamide and suggested that patient compliance and arrhythmia suppression might be improved if NAPA were used to circumvent the inconvenience of the frequent dosing schedule that has been recommended for procainamide.

From the standpoint of managing individual patients with NAPA, the pharmacokinetics of this drug continue to provide the scientific basis for designing dose regimens that will have maximal antiarrhythmic efficacy and minimal toxicity. This review summarizes the salient features of NAPA pharmacokinetics and outlines an approach for individualizing therapy with this drug.