Serum Drug Concentrations in Patients with Ischemic Heart Disease After Administration of a Sustained Release Procainamide Preparation

Despite widespread marketing of a sustained release preparation of procainamide hydrochloride (PROCAN-SR, Parke-Davis), published literature demonstrating its efficacy in maintaining uniform serum drug levels over a 6-hour dosing interval is derived from only normal healthy volunteers. Thirty-three patients with ischemic heart disease, ages 30-88 years, were administered 1-4g/24 hours (mean dose 34 mg/kg/day) of PROCAN-SR in 4 equally divided doses on a Q6H schedule. After achievement of steady-state equilibrium drug concentration, procainamide and N-acetylprocainamide levels were determined by high-performance liquid chromatography on sera obtained from blood samples drawn 2, 3.5 and 5 hours after an oral dose. Mean maximal procainamide and N-acetylprocainamide serum concentrations were 4.6 +/- 1.8 microgram/ml and 4.2 +/- 2.1 micrograms/ml respectively. Mean minimal concentrations were 3.5 +/- 1.7 microgram/ml and 3.6 +/- 2.0 micrograms/ml respectively. The mean change in drug concentration was small (1.1 microgram/ml procainamide and 0.6 microgram/ml N-acetylprocainamide) with procainamide and N-acetylprocainamide concentrations varying only by 27 and 15 percent respectively. These data demonstrate in a population of patients with ischemic heart disease, that Q6H dosing with a sustained release procainamide hydrochloride preparation (PROCAN-SR, Parke-Davis) is associated with only a small acceptable variation between maximal and minimal serum procainamide and N-acetylprocainamide concentrations. This preparation should, therefore, offer greater patient convenience and compliance without sacrificing antiarrhythmic efficacy.