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Resistance develops to certain flu antivirals

Flu shots still are being promoted as the best way to avoid infection this year.

By Susan J. Landers, amednews staff. Feb. 6, 2006.

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Washington -- Physicians are being asked by the Centers for Disease Control and Prevention not to prescribe two of the four antiviral drugs available to treat or prevent annual influenza, because the circulating virus has become resistant to the drugs.

The CDC found that 91% of the 120 influenza A (H3N2) viruses isolated from patients in 23 states were resistant to amantadine, or Symmetrel, and rimantadine, or Flumadine, which are M2 ion channel inhibitors. This represented a sharp increase from last year, when only 11% were resistant. Fewer than 2% had been resistant the year before.

Amantadine also is used to treat the symptoms of Parkinson's disease, and it should continue to be used for this purpose, according to the CDC.

The antivirals oseltamivir, or Tamiflu, and zanamivir, or Relenza, which are neuraminidase inhibitors, are still effective against the flu and may be prescribed for treatment or prevention, according to the CDC.

"This is certainly unexpected news, as we now have to remove a few tools from our tool box that we use to combat influenza," said CDC Director Julie Gerberding, MD, MPH, in announcing the recommendation Jan. 14. "Thankfully, we still have antivirals available that work, but this new development serves as a reminder of the importance of getting people vaccinated to prevent them from getting influenza in the first place."

Flu activity may be starting to pick up across the country, according to the agency, with 18 states reporting either widespread or regional activity. People who have not yet had a flu shot are still urged to get vaccinated, as the virus is expected to circulate for the next several months. More than 80 million doses of vaccine have been distributed, and supplies vary from region to region. The CDC has 3.5 million additional doses available from its stockpile to sell through manufacturers. Plus, manufacturers also still have some available.