A sialic acid-analogue neuraminidase inhibitor with antiviral activity. Administered into the respiratory tract by aerosol inhalation, zanamivir selectively binds to and inhibits influenza A and B virus neuraminidase-mediated cleavage of sialic acid residues in host cell membrane-bound glycoprotein receptors for influenza viruses, preventing the release of progeny viruses from host cell surfaces and, so, further viral replication. OR A drug used to prevent and to treat influenza virus infections. It blocks the release of the virus from infected cells. It is a type of antiviral agent. Also called Relenza.