Interspecies scaling of tebufelone pharmacokinetic data and application to preclinical toxicology

Retrospective application of allometric scaling techniques to tebufelone, a nonsteroidal antiinflammatory agent, in order to better understand the systemic exposure relationships between the doses administered to the species used in toxicology studies and the doses given to human subjects and patients in clinical studies.

Non-compartmental estimates of tebufelone's total body volume of distribution during the terminal phase (Vz) and clearance (CL) obtained from intravenous dosing to rat, monkey, dog, and human were allometrically scaled to body weight, and body weight and brain weight, respectively. AUCs determined from single or multiple dose pharmacokinetic studies and from preclinical toxicology studies were plotted versus dose adjusted for bioavailability and divided by allometrically scaled clearance to produce an allometric relationship suggesting a non-linear increase in AUC with dose across the four species.

Segmental linear regression analysis of this relationship indicates a change point associated with an AUC of approximately 2,300 ng-hr/mL. Elevations in serum levels of various liver enzymes or associated signs of hepatic toxicity occur in some, but not all of the animals exposed for more than three weeks in repeat dosing studies at the actual dose that this represents.

The analysis suggests that doses producing tebufelone plasma levels above a certain threshold AUC and duration of exposure to parent tebufelone are associated with increased risks of hepatic effects. Whether this is because metabolic shifts occur at these doses cannot be determined from these data.