This is currently the main method for preventing influenza and its more problematic complications and works by priming the bodies immune system against the virus. They are relatively cheap and safe and the immunity is life-long. Influenza is not fully amenable to this approach due its antigenic changes, and vaccines must be reformulated each year and even then can only provide limited control of influenza.
The two most common anti-viral drugs are amantadine hydrochloride and rimantadine hydrochloride, these are chemically related and can be used for influenza virus A, but not influenza virus B. They are the only compounds licensed for the treatment and prophylaxis of influenza A infection. The addition of a methyl grouping in rimantidine alters the pharmacological distribution of the drug by preventing its entry into the brain and thus avoiding the amantadine side effect of confusion and nightmares. They both work by blocking the ion-channel activity of the viral M2 protein10 that is found only in influenza A, and thus inhibiting the uncoating of influenza A virus after it enters cells. Clinical use of these agents is limited because of the rapid emergence of resistant strains11.
Like Zanamivir, this is an antiviral agent known as an neuraminidase inhibitor. Oseltamivir works in a similar way to Zanamivr against influenza A and B but is more recent and is ingested rather than inhaled. It was developed because oral administration is seen as a more convenient and economical method for treatment and prophylaxis than inhaled for a possible influenza epidemic in the future. Relenza cannot be administered orally as a result of poor bioavailability and rapid excretion. Oseltamivir is not so selective towards influenza B as it is influenza A.