The antiviral medicines oseltamivir and zanamivir are used to prevent and treat influenza A and B infections. They can reduce the severity and shorten the duration of flu symptoms. Amantadine and rimantadine have been used to help prevent and treat the flu caused by influenza A (but not influenza B) infection. But for the past few years the U.S. Centers for Disease Control and Prevention (CDC) has advised doctors not to use amantadine or rimantadine to treat or prevent the flu. 5 These medicines have not worked against most types of the flu virus.