AIMS:

The aims of this study were to compare the pharmacokinetics of oseltamivir and oseltamivir carboxylate in obese and non-obese individuals and to determine the effect of obesity on the pharmacokinetic properties of oseltamivir and the active antiviral metabolite oseltamivir carboxylate.

METHODS:

The population pharmacokinetic properties of oseltamivir and oseltamivir carboxylate were evaluated in 12 obese (body mass index; BMI ≥30?kg/m² ) and 12 non-obese (BMI <30?kg/m² ) Thai adult volunteers receiving a standard dose of 75?mg and a double dose of 150?mg in a randomised sequence. Concentration-time data were collected and analysed with nonlinear mixed-effects modelling.

RESULTS:

The pharmacokinetics of oseltamivir and its active metabolite, oseltamivir carboxylate, were described simultaneously by first-order absorption, with a one-compartment disposition model for oseltamivir followed by a metabolism compartment and one-compartment disposition of oseltamivir carboxylate. Creatinine clearance was a significant predictor of oseltamivir carboxylate clearance (3.84% increase for each 10?mL/min increase of creatinine clearance, 95% confidence interval [95% CI] of 0.178 to 8.02%). Obese individuals had an approximately 25% (95% CI of 24% to 28%) higher oseltamivir clearance, 20% higher oseltamivir volume of distribution (95% CI of 19% to 23%) and 10% higher oseltamivir carboxylate clearance (95% CI of 9% to 11%) compared to non-obese individuals. However, these altered pharmacokinetic properties were small and did not change the overall exposure to oseltamivir carboxylate.