JAPANESE health authorities are investigating a flu medication also available in Australia after a teenager who took it jumped 11 storeys to his death - at least the 18th juvenile fatality linked to the drug in 17 months.

The Ministry of Health, Labor and Welfare has asked the Japanese importer of Tamiflu, an anti-viral drug regarded as the most important shield against bird flu in humans, to collect information about the conditions of patients who take it.

The 14-year-old boy's death follows a similar case two weeks ago when a girl of the same age died after jumping from an apartment building at Gamagori in central Japan.

It also comes after a warning by the US Food and Drug Administration late last year about the potential dangers of giving Tamiflu to children. The drug is being stockpiled in Australia and elsewhere as the first line of defence against bird flu.

In Australia, as in Japan, it is only available by prescription.

The Swiss manufacturer, Roche, insists the rate of deaths and psychiatric disturbances among people taking it is no higher than for flu sufferers generally. It says there is no evidence of a direct correlation between the drug and the deaths.

In the latest case, the teenager, from Sendai in Japan's north-east, had been prescribed a five-day course of Tamiflu by his doctor. After taking two tablets on Monday, he woke during the evening and told his mother he was going to the bathroom, but went out the front door instead.

His mother followed him and called out when she saw him climbing a waist-high handrail. Police said he did not respond, throwing himself off to the car park below.

The Minister of Health, Labor and Welfare, Hakuo Yanagisawa, urged the public not to rush to conclusions.

"We must consider the matter from a professional point of view because the cause-and-effect relationship has yet to be appropriately established," Mr Yanagisawa said. "There needs to be clear evidence."

He added that if further information came to light, the ministry would consider advising flu sufferers to exercise caution in taking the medication.

Drug companies reported that 54 people using Tamiflu died in Japan before November last year, the ministry said.

Most of the deaths were caused by shock, liver damage or other physical ailments. But in the case of children, they appeared to have been caused during episodes of abnormal behaviour.

There have also been dozens of cases worldwide in which the drug is reported to have induced bouts of psychosis and hallucinations in children.

In an earlier case in Japan, a 17-year-old boy who had taken Tamiflu before going to bed had walked out of the house and stood in front of an oncoming truck. The truck driver told police the boy was smiling at the moment of impact.

Roche is increasing Tamiflu production to 300 million doses a year to meet demand from countries anxious about a bird flu pandemic. In Indonesia, 63 people are known to have died of the disease.