Abstract

Current study was undertaken in order to determine model biopharmaceutical constants for carbamazepine immediate release tablets (200 mg) from documented data of plasma concentration vs time curves. The constants and the proposed methodology simplify bioequivalence determinations to blood sampling restricted only to two time points. Twelve volunteer drug plasma concentration (Cp) determinations from a crossover design bioequivalence study were fitted into equations containing two rate processes. The optimized rate constants were used to generate the Cp vs time curves (generated curves). Generated curves were then differentiated (dCp/dt ) to obtain the first derivative curve for each volunteer from which times for highest rate of absorption (TAmaxn) and highest rate of elimination (TEmaxn) were determined. The corresponding highest rate of absorption and the highest rate of elimination for each individual were then obtained from the generated curve and named as Amaxn and Emaxn. Individual Amaxn and Emaxn values were then averaged to obtain the mean Amax and Emax. Out of the 24 determinations, a total of 13 Amaxn and 20 Emaxn values fell within ±20% of the overall mean. Final Amax and Emax values ware arrived at by averaging each set of individual 13 values and 20 values respectively. From these two mean coordinates, the corresponding constants, plasma drug concentration at the point of highest rate of absorption (CpAmax) and corresponding time TAmax, as well as the plasma drug concentration at the point of highest rate of elimination (CpEmax) and the corresponding time TEmax, were determined.