The Metabolism and Transplacental Transfer of Oseltamivir in the Ex Vivo Human Model

UNLABELLED: Oseltamivir phosphate is extensively metabolized in the ex vivo human placenta model, and the transplacental passage of the metabolite oseltamivir carboxylate is incomplete. OBJECTIVE: To evaluate the metabolism and transplacental transfer of oseltamivir (Tamiflu) in the ex vivo human placental model. STUDY DESIGN: Perfusion studies were performed in six placentas from term, uncomplicated deliveries. Concentrations of oseltamivir phosphate (OP) that were 5-6 fold, 20-30 fold, and 600-800 fold above the therapeutic peak were tested, as neither OP nor its active metabolite, oseltamivir carboxylate (OC), could be detected at near-therapeutic concentrations. The transplacental transfer and accumulation of OC were assessed using the (14)C antipyrine reference method. RESULTS: OP was extensively metabolized to OC. In the 4 placentas with the highest concentration of OP, OC had a mean clearance index of 0.13 +/- 0.08, suggesting that transplacental passage occurs at a relatively low rate. Measurable fetal accumulation occurred in the two placentas with the highest initial concentrations. CONCLUSIONS: Oseltamivir phosphate was extensively metabolized in the ex vivo model. Transplacental transfer of the metabolite was incomplete and accumulation was minimal.