Friday, January 9, 2009

CDC Statement on Oseltamivir (Tamiflu®) Resistance and Antiviral Recommendations

On December 19, 2008, CDC issued interim guidance for health care professionals on the use of influenza antiviral medications this flu season. The guidance was issued in response to early data from a limited number of states indicating that a high proportion of influenza A (H1N1) viruses are resistant to the influenza antiviral medication oseltamivir (Tamiflu®). Worldwide, the proportion of H1N1 viruses that are resistant to oseltamivir has been increasing so this development is not surprising.

Recent media reports may have led some to believe that these developments mean physicians are without influenza treatment options for the 2008-2009 flu season.

At this time, it’s not possible to predict how common H1N1 viruses will be during the rest of this flu season, as there are many different flu viruses and every influenza season is different. The current samples studied come from a handful of states, and may not be indicative of how the rest of the season will progress or what viruses will circulate in other states. However the circulation of oseltamivir-resistant viruses does have treatment implications for health care professionals. CDC is continuing to monitor this situation very closely, but has issued interim guidance for health care professionals to guide their treatment decisions in the current situation.

In fact, the interim CDC guidance provides advice for clinicians on how to treat patients with influenza antiviral medications this season. Clinicians can use influenza test results and information, if available, about which viruses are circulating, to help decide which antiviral(s) should be used. If H1N1 viruses are circulating in the community, or it’s not clear which viruses are circulating, health care providers are recommended to use an alternative antiviral, zanamivir (Relenza®), or to use combination therapy of oseltamivir and rimantadine. Use of zanamivir or dual therapy with oseltamivir and rimantadine would provide effective treatment against all circulating influenza viruses. In some instances, oseltamivir alone can still be used, such as when influenza B is diagnosed, or H1N1 viruses are not circulating.

It is important to remember that CDC recommends annual influenza vaccination as the first and best step in preventing the flu. It is not too late to get vaccinated and this year′s influenza vaccine is expected to be effective against currently circulating oseltamivir-resistant influenza A (H1N1) viruses.

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