Oseltamivir pharmacokinetics in critically ill adults receiving extracorporeal membrane oxygenation support

Extracorporeal membrane oxygenation (ECMO) is known to affect pharmacokinetics and hence optimum dosing. The aim of this open label, prospective study was to investigate the pharmacokinetics of oseltamivir (prodrug) and oseltamivir carboxylate (active metabolite) during ECMO. Fourteen adult patients with suspected or confirmed H1N1 influenza were enrolled in the study. Oseltamivir 75 mg was enterally administered twice daily and blood samples for pharmacokinetic assessment were taken on day 1 and 5. A multi-compartmental model to describe the pharmacokinetics of oseltamivir and oseltamivir carboxylate was developed using a nonlinear mixed effects modelling approach. The median (range) clearance of oseltamivir carboxylate was 15.8 (4.8-36.6) l/hour, lower than the reported mean value of 21.5 l/hour in healthy adults. The median (range) steady state volume of distribution of oseltamivir carboxylate was 179 (61-436) litres, much greater than healthy adults but similar to previous reports in critically ill patients. Substantial 'between subject' variability in systemic exposure to oseltamivir carboxylate was revealed; median (range) area under the curve and C_max were 4346 (644-13660) ng/hour/ml and 509 (54- 1277) ng/ml, respectively. Both area under the curve and C_max were significantly correlated with serum creatinine (r2=0.37, P=0.02 and r2=0.29, P=0.02, respectively). Systemic exposure to oseltamivir carboxylate following the administration of enteral oseltamivir 75 mg twice daily in adult ECMO patients is comparable to those in ambulatory patients and far in excess of concentrations required to maximally inhibit neuraminidase activity of the H1N1 virus. Dosage adjustment for ECMO, per se, appears not to be necessary; however, doses should be reduced in patients with renal dysfunction.