Pharmacokinetic and Bioequivalent Study of a Generic Metoprolol Tablet Preparation

Abstract

A study was conducted to compare the in vivo bioavailability of a generic metoprolol tablet preparation (Metoprolol®) with that of the innovator product, Betaloc®. Both preparations have a labeled dose of 100 mg metoprolol tartrate. Twelve healthy adult male volunteers participated in the study, which was conducted according to a standard two-way crossover design with a washout period of I week. The bioavailability was compared using the total area under the plasma level versus time curve (AUC₀-∞_oo), peak plasma concentration (C_max), and time to reach peak plasma concentration (T_max). No statistically significant difference was observed between the logarithmically transformed AUC₀-_oo values or the logarithmically transformed C_max values of the two preparations. However, a statistically significant difference was observed between the T_max values, but may not be therapeutically significant or important. Moreover, the 90% confidence interval (CI) for the ratio of the logarithmically transformed AUC₀-_oo values of Metoprolol over those of Betaloc was calculated to be between 0.94 and 1.02, while that of C_max was between 0.98 and 1.01, both of which are within the acceptable limit of 0.80-1.25. From the data obtained, it was also observed that a high proportion of our volunteers of Asian origin appeared to be poor metabolizers of metoprolol, which was consistent with what had been observed in our previous study of another preparation of metoprolol.