Zanamivir(generic name - relenza) is an antiviral medication. It blocks the actions of viruses in your body. Zanamivir is used to treat flu symptoms caused by influenza virus in patients who have had symptoms for less than 2 days. Zanamivir may also be given to prevent influenza in people who may be exposed but do not yet have symptoms. Zanamivir will not treat the common cold. Zanamivir may also be used for purposes other than those listed in this medication guide.