US says two flu drugs unlikely to work
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U.S. doctors should stop using two antiviral drugs to treat this season’s influenza because the dominant strain has become resistant to the drugs, health officials said on Saturday.
The alert about antiviral pills amantadine and rimantadine applies to the seasonal influenza, not the H5N1 avian flu strain that experts fear could mutate and cause a global pandemic.
Tests of 120 samples of the H3N2 flu strain—the major one causing flu illness in the United States—showed it was resistant to amantadine and rimantadine in 91 percent of cases, Centers for Disease Control and Prevention Director Julie Gerberding said.
Only 11 percent of cases were resistant to the two drugs during the last flu season.
“Physicians should not use amantadine and rimantadine to prevent flu or to treat patients suspected of having influenza because the drugs will not be effective,” Gerberding said at a news conference.
Doctors instead should prescribe either of two newer medicines, Tamiflu or Relenza, which still fight the strain, she said.
Amantadine and rimantadine are generic medicines used less often than the newer drugs. The older medicines are cheaper and sometimes prescribed to nursing home patients during a flu outbreak to prevent infection.
“We don’t think this (new advice) is going to affect a large number of patients because not many patients are typically treated with amantadine and rimantadine,” Gerberding said.
Still, officials thought it was important to hold a Saturday news conference to get their advice out quickly, she said.
It was unclear whether the flu virus spontaneously mutated or if something else caused the spike in resistance, Gerberding said. Some experts think over-the-counter sales of the drugs overseas may have increased exposure enough for the virus to adapt and evade the medicines.
Flu cases are now widespread in seven U.S. states, mostly in the South and Southwest regions, Gerberding said, adding it was too early to say if this year’s outbreak had peaked.
Tamiflu and Relenza are in demand globally as countries rush to stockpile them in case the avian flu virus mutates to a form that is highly lethal and easy to transmit among people.
Gerberding said there was enough supply of both to meet the needs for the regular flu this season.
Roche AG sells Tamiflu, and developer Gilead Sciences Inc. receive royalties on the drug’s sales. Relenza, which must be inhaled, is sold by GlaxoSmithKline Plc. It was developed by Biota Holdings Ltd.
Tamiflu is known generically as oseltamivir and Relenza as zanamivir.
Several generic makers sell amantadine and rimantadine.
Vaccines to prevent flu infection still are available, officials said.
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