Procainamide elimination kinetics in pediatric patients

Procainamide kinetics were studied in six children after a single intravenous dose. Two-compartment kinetic analysis of serum concentration-time curves of five children, who received a dose of 5.5 ± 0.9 mg/kg (mean ± SD), revealed the following values for kinetic parameters: distribution half-life, 10.3 ± 3.4 min; elimination half-life, 1.7 ± 0.1 hr; elimination constant, 1.2 ± 0.3 hr^-1; plasma clearance 19.4 ± 2.0 ml/min/kg, and steady-state volume of distribution, 2.2 ± 0.3 l/kg. A sixth patient, who received an accidental overdose of 28 mg/kg, had altered elimination kinetics due to drug-induced hypotension. N-acetylprocainamide (NAPA) was detected in serum samples obtained soon after procainamide dosing and peak concentrations were attained at 1 to 2 hr. NAPA levels were lower than corresponding procainamide concentrations at most sampling periods. The findings of short elimination half-life and rapid plasma clearance of procainamide in children suggest that continuous intravenous infusion may be necessary to maintain therapeutically effective plasma concentrations in these patients.