The government, for the first time, is urging doctors not to prescribe two antiviral drugs commonly used to fight influenza because of concerns about drug resistance, officials announced Saturday.
The Centers for Disease Control and Prevention said the recommendation covers the drugs rimantadine and amantadine for the 2006 flu season.
Results of recent lab tests on influenza samples showed that the predominant strain this season — the H3N2 influenza strain — was resistant to the drugs, the agency said.
“Clinicians should not use rimantadine and amantadine ... because the drugs will not be effective,” said CDC director Dr. Julie Gerberding. The two drugs have been used for years to combat type-A influenza.
Gerberding said the lab data, which CDC scientists had been analyzing since Friday, surprised health officials and the health agency rushed to get the word out Saturday.
“I don’t think we were expecting it to be so dramatic so quickly this year,” Gerberding said. “We just didn’t feel it was responsible to wait three more days during a holiday weekend to let clinicians know.”
The CDC tested 120 influenza A virus samples from the H3N2 strain and found that 91 percent, or 109, were resistant to the two drugs. Two years ago, less than 2 percent of the samples were resistant. Last year, 11 percent were, the CDC said.
Mutation, overuse may have caused resistance
Gerberding said the agency was not sure how the resistance occurred, saying it may have been the result of a mutation in the H3N2 flu strain or could have come from overuse of the drugs abroad, such as in countries that permit them drugs to be purchased without a prescription.
One flu expert, Dr. William Schaffner of Vanderbilt University, said the development was “disconcerting” as flu now has joined the ranks of other diseases, such as tuberculosis and HIV, that recently have acquired the ability to resist front-line medications.
But Schaffner said doctors have other options to fight influenza.
One is the antiviral Tamiflu, also known as oseltamivir. The CDC said that all H3 and H1 influenza viruses the agency has tested so far are susceptible to the other commonly used antivirals, including Tamiflu and zanamivir, also called Relenza.
“Tamiflu is now readily available everywhere — in most places, it is the primary antiviral being used” against flu, Schaffner said. “But we’re always a bit frustrated when one of the therapeutic agents is foreclosed. It makes every infectious disease doctor worry a little bit.”
Doctors also recommend an annual flu shot to help prevent getting influenza in the first place.
The CDC said it planned to alert doctors throughout the country via its emergency Health Alert Network and through a special edition of its weekly journal, the Morbidity and Mortality Weekly Report.
Each year, the flu kills about 36,000 people, and some 200,000 are hospitalized because of it in the United States, the CDC said. As of Dec. 31, the latest CDC data available, flu activity was only considered widespread in seven U.S. states, mainly in the Southwest and West: Texas, New Mexico, Arizona, Colorado, Utah, Nevada and California.
On the Net:
CDC flu info: http://www.cdc.gov/flu
Rimantadine info: http://www.nlm.nih.gov/medlineplus/druginfo/medmaster/a698029.html
Amantadine info: http://www.nlm.nih.gov/medlineplus/druginfo/uspdi/202024.html