Comparative bioavailability of two tablet formulations of acyclovir in healthy volunteers

This investigation was carried out to evaluate the bioavailability of a new tablet formulation of acyclovir (400 mg), Clovir, relative to reference product, Zovirax (400 mg) tablets. The 2 brands were found to be similar in weight variation, disintegration time, dissolution, and assay as stipulated by the USPXXIII, as well as by the manufacturer. The bioavailability was carried out on 24 healthy male volunteers who received a single dose (400 mg) of the test (T) and the reference (R) products in the fasting state, in a randomized balanced 2-way crossover design. After dosing, serial blood samples were collected for a period of 16 hours. Plasma harvested from blood was analyzed for acyclovir by a sensitive and validated high-performance liquid chromatographic assay. The maximum plasma concentration (Cmax), area under the plasma concentration-time curve up to the last measurable concentration (AUC0-t), and to infinity (AUC0-infinity), and the absorption rate (Cmax/AUC0-infinity) were analyzed statistically under the assumption of a multiplicative model. The time to maximum concentration (Tmax) was analyzed assuming an additive model. The parametric confidence intervals (90%) of the mean values of the pharmacokinetic characteristics (AUC0-t, AUC0-infinity, Cmax, Cmax/AUC0-infinity) for T/R ratio were in each case, well within the bioequivalence acceptable range of 80-125%. The test formulation was found bioequivalent to the reference formulation by the Schuirmann's two 1-sided t tests and by Wilcoxon Mann Whitney two 1-sided tests procedure. Therefore, the 2 formulations were considered to be bioequivalent.