Feasibility of interspecies extrapolation in determining the bioequivalence of animal products intended for intramuscular administration

To examine the validity of extrapolating parenteral product bioequivalence determinations across target animal species, the relative bioavailability o f two injectable formulations of ampicillin trihydrate (Polynex(R), a water -based suspension, and Ampi-kel 10(R), an oil-based suspension) was examine d in calves, sheep and swine. Employing products recognized to be bioinequi valent provided an opportunity to explore potential species-by-formulation interactions. As compared with Polyflex(R), Ampi-kel 10(R) exhibited lower area under the curve (AUC) estimates but higher peak concentrations in all target animal species. Nevertheless, marked interspecies differences were n oted in the width and bounds of the confidence intervals about the differen ces in treatment means. Potential physiological and physico-chemical reason s for these findings are discussed.