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Study: Drug not working against flu

kira86 于2009-03-04发布 l 已有人浏览
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An important antiviral drug no longer works against this season's most prevalent type of flu, which

An important antiviral drug no longer works against this season's most prevalent type of flu, which has mutated into a resistant strain, researchers reported today in the Journal of the American Medical Association.

That drug -- sold as Tamiflu in the U.S. -- was one arrow in a very small quiver of antiviral medicines used to battle influenza, an illness that lands 200,000 Americans in the hospital and kills 36,000 every year, according to the Centers for Disease Control.

Public health officials and physicians called the development and spread of Tamiflu-resistant flu disturbing.

"It makes me nervous," said Michael Koller, a doctor of internal medicine at Loyola University Medical Center. "We know that it keeps mutating and that is why it is still around. It manages to figure out ways to outsmart us and our medications."

With Tamiflu no longer effective against this particular flu strain, known as H1N1, physicians are turning to zanamivir, which has problems of its own. The drug, which is inhaled, is not recommended for some of the very populations that would need it most – very young children and people with respiratory problems."

For those people, CDC officials recommend a combination of Tamiflu and another antiviral called rimantadine, which was the subject of a flu resistance scare of its own in 2006.

"The problem is that we now have different flu strains that are susceptible to different antiviral agents, and clinicians often do not know what strain is infecting a person. The new recommendations try to account for these different factors," said Alicia Fry, a medical epidemiologist in the influenza division of the CDC and a co-author of the JAMA report.

With so many problems with the antivirals, public health officials are urging people to get a flu shot, which offers good protection this year against the H1N1 strain.

"Flu season is still peaking," said Koller, who noted that he started seeing a rise in flu patients around the first week of February. "There is no sign we are on our way down. It is not too late."

One of the virus' most astounding feats is that it managed to mutate into a resistant form and spread around the globe in a year.

Scientists began picking up hints that was happening during the last flu season, when reports came in from Canada to Russia to Hong Kong to the U.S. of Tamiflu-resistant flu. In the U.S., scientists found that about 11 percent of the H1N1 viruses were resistant.

By summer, South Africa ominously reported all of its H1N1 was resistant. And now that is the case in the U.S. "That is a phenomenal change in one year's time," Koller said. "It is very concerning."

The alarming change in the virus upended some assumptions about it. For one, scientists had long believed that H1N1 could never become resistant to Tamiflu.

That's because the drug was designed to target a part of the virus that couldn't mutate without, essentially, killing it. That part was supposed to be bulletproof -- if it mutated, the virus would blow up. If it didn't, Tamiflu would work.

That assumption turned out to be wrong. The virus mutated and is surviving quite well.

The other assumption turned on its head was that resistance to a drug like Tamiflu would be a result of exposure to the drug, not unlike the way heavy antibiotic use leads to antibiotic resistance.

But that didn't turn out to be right, either.

Norway, a country with a lot of Tamiflu-resistant flu, hardly uses the drug. And Japan, a country that uses Tamiflu a lot, had hardly any resistant flu.

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Scientists believe what happened is that Tamiflu got a lucky break, mutating by luck into a form that turned out to be resistant to our biggest weapon against it. "This is what is so amazing," said Vincent Racaniello, a professor of microbiology at Columbia University Medical Center. "This arose spontaneously."

The news on the flu front is not all bad, though.

Two different sets of scientists recently announced they had found antibodies that seem to attack a part of the flu virus that most strains share in common, which means a universal vaccine that won't have to change year to year might be within grasp for the first time.

"That is really exciting," said Racaniello, who also writes a blog, Virology. "That will probably pan out in five to 10 years."

And for most of us, antiviral drugs like Tamiflu wouldn't help much anyway. For most, the flu is like a very hot, very fast-moving wildfire.

By the time you feel really sick, get to the doctor and then hoof it to a drug store and start taking the drug, the flu is likely to be almost burned out, leaving a scorched earth of fever, chills and other symptoms.

That lingering few weeks of sickness is your body dealing with the smoldering aftermath – the immune response, the damage to your respiratory system, the weakness from being so ill.

And that's why healthy people would need to take an antiviral within 48 hours of falling sick to get relief, said David Weinstock, an assistant professor at Harvard Medical School and a co-author of an editorial accompanying the JAMA study.

"But that is not the same thing as if your grandma was living in a nursing home and developed a severe infection from influenza and it had been more than 48 hours," Weinstock said. "There is a lot of common sense to tell you it would help."

And those are the people – the 90-year-old grandmother in the nursing home, the 11-month old baby – that die from the flu each year, and need antiviral help.

But because the different strains wax and wane from year to year, H1N1 could virtually disappear next season and another, one more susceptible to antivirals, could be dominant, Racaniello said.

"We don't know what will happen from year to year," he said. "One thing I have learned is you can't predict."

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