The quantitative disposition of procainamide and N-acetylprocainamide in the rat

The objectives of this study were to investigate: 1) the rat acetylator phenotype, 2) the systemic availability of oral procainamide (PA), 3) the kinetic disposition of PA and its N-acetyl metabolite (NAPA) and 4) the relationship between PA dose and steady-state blood PA and NAPA levels. The rat acetylator phenotype seems to be monomorphic in type. The systemic availability of PA was estimated to be 78%. The half-life (T 1/2) of PA elimination was 55 minutes and that of NAPA was 51 minutes. PA clearance was 64 ml/kg/min and NAPA clearance 22.4 ml/kg/min. The apparent distribution volume for PA was 4.92 liters/kg and for NAPA 1.64 liters/kg. Acetylation accounted for 38% of PA disposition, urinary excretion 34% and other metabolism 28%. Urinary excretion of NAPA accounted for 72% of administered drug. Steady-state blood PA levels showed a linear increase with dose whereas NAPA did not. The latter observation suggests saturation of PA acetylation at higher PA doses.