Oseltamivir is an antiviral neuraminidase inhibitor with potent and selective competitive inhibition of the influenza virus neuraminidase, an enzyme necessary for viral replication. Oseltamivir phosphate is an inactive prodrug that exerts pharmacologic activity when hydrolyzed in vivo to the active form, oseltamivir carboxylate. This activated form interferes with the release of progeny influenza virus from infected host cells and halts the spread of infection to new host cells. Oseltamivir reduces the duration of shedding and the viral titer and can shorten the length of symptoms by 0.5 to 3 days.