Reports of abnormal behaviour sends Tamiflu back to the drawing board

The manufacturers of the bird flu drug Tamiflu are about to repeat basic research and clinical trials on the high profile influenza drug.

Swiss drug maker Roche and Japanese partner Chugai will conduct the new research following reports of a possible link to abnormal behaviour in teenagers.

Tamiflu has been under intense scrutiny in Japan following cases of young people jumping from buildings after taking the drug.

Tamiflu is being stockpiled around the world because it is considered the best first line treatment option currently available should there be a bird flu epidemic.

The new research on the antiviral has been called for by the Japanese health ministry amid fears that it may have been linked to several teenagers who killed or harmed themselves during episodes of extreme mental disorder.

In February this year a boy and a girl, both 14, fell to their deaths after taking the drug.

Although the Japanese health ministry says there was no evidence of a causal link between Tamiflu and the behaviour they have ordered doctors not to prescribe it to teenagers, unless they are suffering from extreme flu symptoms.

The ministry has advised Roche and Chugai to begin pre-clinical and human clinical trials to establish whether Tamiflu could be linked to side-effects such as delirium and delusion.

The Japanese also plan to launch their own full investigation into whether there was a causal link between the drug and psychiatric problems.

Of 1,268 cases of patients experiencing side effects after taking Tamiflu, 183 of them, mostly young people, were classified by the ministry as having shown abnormal behaviour.

Both Roche and Chugai deny any such link and doctors say influenza itself can cause abnormal behaviour.

Tamiflu has been used by 45 million people in 80 countries since it went on the market in 1999; some 35 million people in Japan have taken Tamiflu, which equates to around 70 percent of the world's Tamiflu consumption.

Although it is rare for a drug maker to return to animal research after a drug has been on the market, Chugai says Roche will conduct additional pre-clinical research on Tamiflu, including toxicity studies in rats to look at the effect of the drug on the brain.

Chugai will also conduct clinical research on the effects of Tamiflu on sleep.

The time period involved is from early 2001, when Chugai began selling the drug, until April 17th of this year.

To date there have been eight cases of deaths after possibly abnormal behaviour, seventy people have died after taking the drug and there have been 26 cases of people either jumping off or falling from buildings or other heights, 22 of whom were teens.

Chugai said its study would be conducted on 12 to 30 human volunteers and would be completed by the end of December.

Meanwhile an interim report will be presented by the end of September.