Current Treatments for Influenza:
Antiviral Medications
Currently, there are four influenza antiviral drugs approved for use in the United States: Tamiflu®) (Oseltamivir), Relenza® (zanamivir), Symmetrel® (amantadine), and Flumadine® (rimantadine). Symmetrel and Flumadine are inhibitors of the M2 viral channel while Tamiflu and Relenza inhibit the viral neuraminidase enzyme. The first M2 blocker amantadine was introduced to the market in 1967 followed by the second M2 blocker, rimantadine, 26 years later. Amantadine and rimantadine are related antiviral medications that block the M2 ion channels which mediate the uncoating of the viral particle inside the host cell. Due to the increasing rate of resistance to the adamantanes in recent years, the predominant type of antiviral drug currently used for the treatment and prophylaxis of influenza are the neuraminidase inhibitors, oseltamivir and zanamivir. These drugs are sialic acid analogues which bind to the viral NA and thereby interfere with the release of new influenza virus particles from infected cells. However, like the adamantanes, oseltamivir resistance has grown among seasonal influenza strains. By the end of the 2008-09 flu season, the World Health Organization reported ~95% of all seasonal H1N1 viruses tested were resistant to oseltamivir and worldwide oseltamivir resistance to the pandemic H1N1 2009 virus has reached ~1.5%. This is especially concerning because it took only two years for worldwide seasonal H1N1 oseltamivir resistance to go from <0.5% to >95%. Experience with other viral enzyme inhibitors such as the HIV protease inhibitors would indicate that the need for alternative therapies will likely increase. (http://www.who.int/csr/disease/influenza/H1N1webupdate20090318%20ed_ns.pdf)
Vaccines
Inactivated or attenuated live human influenza vaccines are in worldwide use, especially for high-risk groups. However, due to constant viral mutation, vaccines need to be updated and modified yearly to maintain efficacy. They are not 100% effective when administered, they take 2-3 weeks to become effective (so they cannot be used for acute illness), and higher risk patients, e.g. the elderly and the immune-compromised often have poor responses. Moreover, not all people will have access or will get a vaccine. For these reasons, there are significant medical and market needs for therapeutic treatments for influenza in addition to vaccines