An inhibitor of influenza neuraminidases and an active metabolite of laninamivir octanoate; inhibits the neuraminidases from influenza A H1N1, H2N2, and H3N2 strains (mean IC50s = 2.49, 11.4, and 16.7 nM, respectively) and influenza B Victoria and Yamagata strains (mean IC50s = 18.9 nM for both); increases survival in a mouse model of lethal influenza H1N1 infection when administered intranasally at 69 UG/kg