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.