Comparative bioavailability of two oral sustained-release procainamide products.

The bioavailability characteristics of two sustained-release oral procainamide preparations, Procan SR and Pronestyl-SR, were compared in 10 patients with arrhythmias. Each patient was randomly assigned to receive either Procan SR 1 g or Pronestyl-SR 1 g, both administered orally every six hours. The initial drug was continued for 48 hours (eight doses), at which time the second drug, given at the same dosage and dosing interval, was substituted for a 48-hour period. Serum samples for procainamide determination were obtained hourly between 42 and 48 and between 90 and 96 hours after initiation of procainamide therapy. Values for area under the serum concentration-time curve (AUC) during the steady-state dosing interval, maximum serum drug concentration (Cmax), minimum serum drug concentration (Cmin), Cmax:Cmin ratio (representing fluctuations in serum drug concentrations within the dosing interval), and the time to maximum serum drug concentration (tmax) were determined. Mean ( +/- S.D.) tmax values for Procan SR and Pronestyl-SR were 2.2 +/- 0.8 hours and 3.8 +/- 1.1 hours, respectively. Only the differences between tmax values were statistically significant. The study had an 83% chance of detecting a 20% difference in AUC values. The chances of detecting a 20% difference in values for Cmax and Cmin were 62% and 71%, respectively. These two preparations would probably possess similar therapeutic properties when given at the same dosage and dosing schedule; however, studies with larger subject populations are needed to project bioavailability data to the general population.