U.S. experts concerned about effectiveness of Tamiflu

18:12' 09/07/2009 (GMT+7)

Amid reports of Tamiflu-resistant H1N1 cases, health officials are concerned about how quickly a new strain of the virus resistant to the drug Tamiflu will spread, or how dangerous it might become.

A man leaves a school, attended by children from the five new confirmed cases of influenza A (H1N1), after collecting a box of Tamiflu in south London May 4, 2009. (Xinhua/Reuters File Photo)

Although, isolated cases of the A/H1N1 virus, seem mild for now, but future remains uncertain, the Health Day News reported on Wednesday

So far, three people have been stricken in recent weeks by a resistant strain of the new H1N1 flu virus -- one in the United States, one in Denmark and one in Japan, according to earlier press reports.

In all three cases, the illnesses were mild and all of the patients recovered.

More widespread resistance could come from one of two scenarios, John J. Treanor, professor of medicine and of microbiology and immunology at the University of Rochester Medical Center in New York, said in remarks published by Health Day News.

The first would be if the virus develops mutations in people who are being treated with Tamiflu and then spreads to others, Treanor said.

The second would involve a random genetic reassortment, in which the new swine flu and the seasonal flu exchange genes, he said.

"The current seasonal viruses are resistant to Tamiflu," Treanor noted. "We could see a get-together resulting in a hybrid which ... potentially could be able to infect people more easily."

"This is not unexpected, but it's very unpredictable whether this will end up spreading," said Treanor.

"There is certainly a potential for the novel H1N1 viruses to develop resistance to oseltamivir (Tamiflu) and for those resistant viruses to become widespread," he added.

"Everyone recognizes that. That is the Achilles' heel of antiviral therapy and it's completely possible that we will see this with the novel H1N1."

"This is expected to a certain extent," agreed Manjusha Gaglani, associate professor of pediatrics at Texas A&M Health Science Center College of Medicine and a pediatric infectious diseases specialist at Scott & White Hospital.

Strains of the "regular" seasonal flu often become resistant to antiviral drugs but, generally speaking, antiviral resistance is less common with Tamiflu and a related antiviral drug, Relenza, than it is with two other drugs, amantadine and rimantadine, which the U.S. Centers for Disease Control and Prevention has recommended against using for seasonal flu.

Tamiflu is preferred over Relenza in general because it is easier to administer, Gaglani said.

Since there is no vaccine for the H1N1 virus, Tamiflu is the main weapon available in the effort to prevent and treat H1N1 infections.

There has been speculation that overuse of the drug has contributed to the new drug resistance but, at this point, that is another unknown, and people who fall ill do need to be treated, said the report.

"I don't know how much that's being driven by use of the drug," Treanor said. "I think the drug should be used where indicated. If resistance happens, it's going to happen, but we have to use medicine to treat sick people appropriately."

VietNamNet/Xinhuanet