Metoprolol or Propranolol Does Not Alter the Kinetics of Procainamide

Eight healthy volunteers received a single 500 mg intravenous dose of procainamide hydrochloride by 30-min infusion on three occasions in random sequence. The three modes of administration were (a) control, without concurrent drugs; (b) during coadministration of propranolol, 80 mg three times daily; and (c) during coadministration of metoprolol, 100 mg two times daily. Procainamide kinetics were determined from multiple serum concentrations measured by enzyme-multiplied immunoassay (EMIT) during 10 h after each dose. A metaproterenol infusion study verified a high degree of beta-blockade during trials 2 and 3. Mean procainamide half-life during the three trials (1.9, 2.2, and 2.3 h, respectively) tended to show prolongation during beta-blocker treatment, but the overall difference was of borderline significance (0.05 less than p less than 0.1). Total procainamide clearance (16.2, 14.1, and 13.7 ml/min/kg) did not differ significantly between the three trials, nor was there a significant change in area under the serum concentration curve for N-acetylprocainamide, the major metabolite. Thus the kinetics of procainamide in healthy persons are not importantly altered by typical therapeutic doses of two beta-adrenergic blockers.