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Study: Bird Flu Resistance to Tamiflu May be More Common Than Thought

A study on two Vietnamese women who died earlier this year from bird flu indicates that resistance to the antiviral drug Tamiflu might be more common than thought. The patients died despite receiving recommended doses of the drug very early in their infections.

The study by doctors in Ho Chi Minh City raises concern because Tamiflu is the main drug that nations are stockpiling to defend themselves against the virulent H5N1 strain of avian flu. So far, it has killed more than 70 people in South Asia since 2003.

In the study, doctors found that two people who died of bird flu, a Vietnamese mother and her 13-year-old daughter were the victims of a form of the virus that resisted treatment with full doses of Tamiflu given to them only one day after becoming infected.

"Tamiflu may not be adequate in at least a proportion of patients," said Dr. Menno de Jong at the Ho Chi Minh City unit at the Hospital for Tropical Diseases in London.

He is the lead author of the study appearing in the New England Journal of Medicine.

"Resistance to the drug may not occur infrequently to H5N1 influenza since we detected the resistant virus in two of seven patients who we followed throughout the treatment period," he added.

Dr. de Jong and his colleagues say the findings suggest the need for stronger doses of Tamiflu in some bird flu patients or additional antiviral drugs.

In New York City, pediatrician Anna Moscona of the Weill-Cornell Medical College agrees.

"The reason this is so alarming is that right now, we really don't have a lot of options," she explained.

Dr. Moscona says the Ho Chi Minh City study is the latest of several reports indicating growing Tamiflu resistance. The only other drug effective against influenza is Relenza. Fortunately, no virus is yet resistant to it, but the New York pediatrician notes that it is available only in inhaled form, making it less practical than Tamiflu.

"So we are really limited to this one drug. And if we lose the effectiveness of this drug by so many resistant strains that we no longer can use this drug effectively, then we are really in trouble. We have no backup antiviral medication against influenza," she added.

Dr. Moscona warns physicians not to let their patients stockpile Tamiflu, because it is likely to lead to the use of insufficient doses, permitting flu viruses to survive, get stronger, and spread.