To investigate oseltamivir and oseltamivir carboxylate pharmacokinetics in critically ill patients who were receiving continuous venovenous hemodialysis (CVVHD) and/or extracorporeal membrane oxygenation (ECMO).Prospective, open-label, pharmacokinetic study.Intensive care units of an academic medical center.Thirteen critically ill patients aged 13 years or older with suspected or confirmed H1N1 influenza who had a prescription for oseltamivir and were concurrently receiving CVVHD and/or ECMO between October 2009 and January 2010.Oseltamivir 150 mg was administered nasogastrically or nasoenterically every 12 hours