Antiviral management of seasonal and pandemic influenza

The goals of antiviral treatment for influenza are to decrease symptoms and functional disability and, more important, to decrease associated complications, hospitalizations, and mortality. Four drugs have been approved for treatment of and prophylaxis against influenza in the United States, but they are underutilized. The M2 ion channel inhibitors amantadine and rimantadine are effective for prophylaxis, and they decrease the duration of symptoms if they are used for early treatment of influenza A. The rapid emergence of resistance during therapy and, recently, the circulation of resistant H3N2 viruses in the community have decreased the usefulness of these M2 ion channel inhibitors. Early therapy with neuraminidase (NA) inhibitors, either oseltamivir or zanamivir, reduces the duration of symptoms, the duration of disability, and the risk of lower respiratory tract complications. Oseltamivir has been shown to decrease antibiotic use, the number of hospitalizations, and, probably, the risk of death after influenza. NA inhibitors might provide substantial benefits in the treatment of pandemic influenza, with reductions in the numbers of hospitalizations and deaths occurring if such treatment (1) is made available in sufficient time, through rapid distribution, and (2) is available in sufficient quantities as a result of stockpiling. Both of the aforementioned NA inhibitors are highly effective for prophylaxis. Geographically targeted mass chemoprophylaxis might contain the spread of a pandemic virus, but multiple hurdles to successful implementation exist. Resistance to oseltamivir occurs with the H274Y variant in viruses that contain N1; however, to date, such variants have been less fit, have not been transmitted from person to person, and have retained susceptibility to zanamivir. Alternative agents and approaches, including parenteral and combination therapy, for the treatment of influenza are needed in the near and long term.