An inhibitor of influenza neuraminidase (IC50s = 0.09 and 11 nM for influenza A and B neuraminidases, respectively); selective for influenza neuraminidase over bacterial, mammalian, and other viral neuraminidases (IC50s = >300 μM); inhibits neuraminidase activity in H1N1, H2N2, H3N2, and H6N2 influenza strains (IC50s = 0.09-1.1 nM) and reduces lysis of MDCK cells infected with influenza (EC50s = <0.01-21 nM); protects mice against lethal influenza infections when administered prior to infection at a doses ranging from 10-100 mg/kg; increases survival in ferrets infected intranasally with avian influenza type A H5N1 when injected intramuscularly after infection