Researchers warn about overprescribing Tamiflu

LONDON (Reuters) - Sewage systems do not break down Tamiflu, which means the main weapon against bird flu could seep into natural waters and make certain viruses resistant to the drug during a pandemic, Swedish researchers said on Wednesday.

Because of this, doctors should take care to not overprescribe Roche Holding AG's market-leading antiviral drug, they said in a study published in the Public Library of Science.

"Antiviral medicines such as Tamiflu must be used with care and only when the medical situation justifies it," Bjorn Olsen, a researcher at Uppsala University and the University of Kalmar said in a statement.

"Otherwise there is a risk that they will be ineffective when most needed, such as during the next influenza pandemic."

Roche, which the researchers said donated the drug for their study, said it was unlikely such resistance would arise.

"In the highly unlikely event that such resistance was generated, this must be balanced against the fact that influenza viruses with the associated mutational changes have been shown to have lower transmissibility," the company said.

Tamiflu, known generically as oseltamivir, was having lackluster sales as a drug to prevent and treat seasonal flu until it was the first treatment to show real efficacy in helping people with bird flu.

Health experts agree that a pandemic of something is inevitable. They cannot specify the disease, but the H5N1 avian flu virus currently wiping out flocks from Indonesia to Africa and parts of Europe is the main suspect.

It rarely infects people but has killed 201 out of 329 people sickened since the virus re-emerged in Hong Kong in 2003, according to the World Health Organisation.