Oseltamivir acid -13C,d3 (GS 4071-13C,d3; Ro 64-0802-13C,d3) is a 13C- and deuterium-labeled Oseltamivir acid. Oseltamivir acid is the active metabolite of Oseltamivir phosphate and inhibits influenza virus neuraminidase ( IC 50 =2 nM). Oseltamivir acid is orally active and can be used to study influenza A/B infections.