Saturday, December 10, 2005

News - Bird-Flu Patients May Need Higher Dose of Tamiflu (Update1)

Bird-flu patients may need higher doses of the antiviral treatment Tamiflu than recommended by drugmaker Roche Holding AG, World Health Organization officials said.

Tamiflu can reduce the severity and duration of illness caused by seasonal influenza provided it is given within 48 hours of the onset of symptoms. The drug has been used in the treatment of more severe disease caused by the H5N1 strain of avian influenza, and is being stockpiled worldwide as the best protection against any pandemic flu.

Clinical trials may start as early as next month in countries including Vietnam to study whether doubling the recommended dose provides more effective treatment in H5N1 cases, Peter Horby, a Hanoi-based epidemiologist with WHO, said today.

``It's possible that increased doses of Tamiflu for treatment above the current recommended level may be more effective in H5N1 cases,'' Horby said by telephone from Bangkok. ``There are reports of some patients being treated with standard doses of Tamiflu in Vietnam and not being cured.''

Roche is working closely with the WHO and the National Institutes of Health in the U.S. to assist in the evaluation of a higher dose, company spokesman Daniel Piller said. Studies conducted during the drug's development showed higher dosages were safe. The lower dose was just as effective for seasonal flu.

``In terms of the clinical effect of the drug in people infected with H5N1, we have limited information,'' Piller said. ``We will look at longer duration of therapy and higher doses in critical case of H5N1 infected to derive the greatest benefit from Tamiflu for such patients.''


The ministry of Health in Vietnam has already instructed doctors to lengthen the treatment time for Tamiflu to seven days from five days for bird-flu patients, according to Tran Tinh Hien, deputy director of the Hospital for Tropical Diseases in Ho Chi Minh City, which has treated bird-flu patients in the past.

``The bird-flu virus is much more virulent, so it makes sense to double the dose for bird-flu patients,'' the doctor said in an interview. ``Given that Tamiflu has been unsuccessful in treating several cases in the north, I support that trial.''

Avian flu has infected at least 135 people the past two years in Vietnam, Thailand, Indonesia, Cambodia and China and killed 69 of them, Geneva-based WHO said on Dec. 7.

``In some cases in which people were given antiviral drugs, they died even after the treatment,'' Hitoshi Oshitani, Manila- based regional adviser in communicable disease surveillance and response with WHO, said this week. ``We don't know why the antiviral drugs didn't work in these cases. The current recommended dose of antiviral may not be enough to treat H5N1 cases.''

Too Late?

Another explanation may be that the patients began treatment more than 48 hours after their symptoms emerged, Oshitani told the Institute of Southeast Asian Studies on Dec. 6.

``This virus may be causing them more systemic infection so the usual recommended dose of antiviral is based on our experience on usual human influenza infections which only causes respiratory infection,'' he said.

Under the planned schedule for the Tamiflu trial, 150 milligrams of the medicine would be given twice a day for five days, Horby said. That compares with the recommended dose of 75 milligrams twice a day for five days, he said.

``We know that in trials using Tamiflu to treat normal influenza, you can increase the dosage safely,'' Horby said.

Details of the study are yet to be completed. The trials would be the first through a new research network established by the WHO to gather information on H5N1 cases, he said.


There are other reasons why H5N1 patients may require higher doses of Tamiflu, scientists said.

``The virus is multiplying to higher levels than normal human viruses, therefore it may take more drug to control this higher level of virus,'' said Jennifer McKimm-Breschkin, a virologist at Australia's Commonwealth Science and Industrial Research Organization (CSIRO) in Melbourne.

``Some H5N1-infected patients treated with Tamiflu have had resistant virus emerge during the treatment, hence the theory is that higher doses may prevent resistance emerging,'' McKimm- Breschkin said.

To contact the reporters on this story:
Jason Folkmanis in Hanoi;
Jason Gale in Singapore at U.S.


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