Comparative biopharmaceutical performance of imipramine formulations in man

The systemic availability of an investigational liquid formulation of imipramine was compared to that of a commercially available tablet (Tofranil) whose therapeutic efficacy has been established by usage. The experiment was conducted under controlled conditions and a balanced 2-by-2 crossover design was used to dissociate the significance of formulation effects from subject, group, and experimental period sources of variation. Pharmacokinetic interpretation and statistical analysis of plasma concentrations as a function of time and of systemic availability indicators reveal a nearly identical biopharmaceutical behavior for the two preparations. Significant differences (P less than 0.05) were found in the cumulative area under the plasma concentration--time curve (AUC) up to 4 hours after administration and the availability lag time, but not in the maximum plasma concentration, the time at which this concentration is reached, the first-order availability rate constant, and the AUC to infinity. These results collectively indicate a very similar biopharmaceutical performance, where the differences in the early AUC values are partly attributable to a longer availability lag time for the tablet formulation.