Background: Detailed pharmacokinetics to guide oseltamivir (Tamiflu®) dosing in morbidly obese patients is lacking.
Methods: The OPTIMO trial was a single-centre, non-randomized, open-label pharmacokinetic study of single-dose and steady-state oral oseltamivir phosphate and its carboxylate metabolite in healthy, morbidly obese [body mass index (BMI) > 40)] and healthy, non-obese (BMI < 30) subjects.
Results: In the morbidly obese versus control subjects, respectively, the single-dose median oseltamivir oral clearance (CL/F) [840 (range 720-1640) L/h versus 580 (470-1800) L/h] was higher, the area under the curve from time zero to infinity (AUC(0-∞)) [89 (46-104) ng·h/mL versus 132 (42-160) ng·h/mL] was lower and the volume of distribution (V/F) [2320 (900-8210) L versus 1670 (700-7290) L] was unchanged. In the morbidly obese versus control subjects, respectively, the single-dose median oseltamivir carboxylate CL/F [22 (17-40) L/h versus 23 (12-33) L/h], AUC(0-∞) [3100 (1700-4100) ng·h/mL versus 3000 (2100-5900) ng·h/mL] and V/F [200 (130-370) L versus 260 (150-430) L] were similar. Similar results for oseltamivir and oseltamivir carboxylate CL/F, AUC₀₋₁₂ and V/F values were observed in the multiple-dose study.
Conclusions: With single and multiple dosing, the systemic exposure to oseltamivir is decreased but that of oseltamivir carboxylate is largely unchanged. Based on these pharmacokinetic data, an oseltamivir dose adjustment for body weight would not be needed in morbidly obese individuals.