Pharmacokinetics of oseltamivir in breast milk and maternal plasma

Objective: Women in the postpartum period are at high risk for complications from influenza. Pharmacokinetic data of oseltamivir phosphate in postpartum women, however, are lacking. Study Design: Seven healthy patients within 48 hours of delivery were recruited. Each woman received 75 mg of oseltamivir phosphate. Plasma and breast milk samples were obtained at times 0, 0.5, 1, 2, 4, 8, 12, and 24 hours after the first dose. The samples were analyzed for oseltamivir and oseltamivir carboxylate levels. Using a noncompartmental model, area under the curve (AUC), maximum concentration (C_max), time to maximum concentration, and half-life were estimated. Results: Oseltamivir phosphate and oseltamivir carboxylate were found in breast milk, although later and in lower levels than that found in plasma. The C _max and AUC 0-24 was higher for the active metabolite than for the prodrug in both plasma and breast milk. Conclusion: Oseltamivir carboxylate was present in breast milk but in concentrations significantly lower than considered therapeutic in infants.