Most flu resistant to one drug type

Government flu researchers reported more evidence Thursday that most of the Type A flu virus circulating this season is resistant to one class of antiviral drugs often prescribed for flu.

Scientists had known that resistance to the drugs amantadine and rimantadine had been creeping upward over the last decade, and about 11 percent of the viruses tested during last winter's flu season didn't respond to them.

But in the latest testing from the federal Centers for Disease Control and Prevention, published online by The Journal of the American Medical Association, the resistance "was an alarmingly high rate of 92 percent," wrote senior researcher Rich Bright.

"These viruses were isolated from patients residing in 26 states, representing all regions of the United States. This rate was much higher than the rate found among viruses collected in previous seasons," the researchers added.

Based on similar results from testing of just 120 samples by mid-January, the CDC had issued an alert to the nation's doctors not to prescribe the amantadines for the flu any more this season.

The CDC's director, Dr. Julie Gerberding, compared the decision to removing "a few tools from our toolbox that we use to combat influenza," but said, "thankfully, we still have antivirals available that work."

Another review of the effectiveness of flu medicines, published last month in the British medical journal The Lancet, concluded that the two drugs are ineffective against either seasonal or pandemic flu and should also not be used because they can cause severe side effects, such as hallucinations.

The British researchers looked at results of 50 trials on both amantadines and the other class of antiviral, neuraminidase inhibitors, including Tamiflu, and found that while both types of drug could help ease flu symptoms, none prevented infection.

So while Tamiflu has become prized because it has shown some signs of fending off the worst of the spreading avian flu infections passed from birds to humans, Dr. Tom Jefferson of the Cochrane Vaccines Field research center in Rome said the inhibitor should not be used in seasonal flu cases "and should only be used in serious epidemic or pandemic alongside other public health measures such as use of masks, gowns, gloves quarantine and hand-washing."

CDC surveillance through the third week of January shows that the winter flu outbreak started to pick up during the holidays, with infection levels holding steady through much of the past month.

Some parts of the country report that the number of flu cases is already in decline after a mild January, but public health officials fear that a new onslaught from winter could spike infection rates again over the next several weeks and are telling people that they could still benefit from getting a flu shot, which are now more readily available than they were in the fall.

As of Jan. 21, five states were still reporting widespread flu, 23 reported regional flu outbreaks and nine said cases were reported only in some localities.

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On the Net: www.cdc.gov/flu/