A child mimics a rooster in Manila. (AFP)

Tokyo, Nov. 14 (Reuters): Japan’s Chugai Pharmaceutical Company said today it has told the government that two teenage boys exhibited abnormal behaviour that led to their deaths after taking the anti-flu drug Tamiflu, made by Chugai’s Swiss parent Roche Holding AG.

Tamiflu is considered one of the best defences against bird flu in humans and is in great demand as fears grow about the spread of the deadly virus.

The comments from Chugai come in response to weekend news reports that Japan’s health ministry is investigating the deaths of two teenage boys who died in accidents linked to odd behaviour shortly after taking the drug.

In Zurich, Roche said today there was no greater incidence of abnormal behaviour associated with taking Tamiflu than was generally seen in untreated flu patients.

“We do not see an imbalance in these types of neuropsychiatric events for Tamiflu versus the background associated with influenza,” Roche’s head of pandemic sales of the drug, David Reddy, said.

The Japanese health ministry said it had instructed the drug maker last year to alert doctors to possible side effects such as abnormal behaviour and that it had no plans to issue a fresh warning.

Shares of Chugai lost 2.6 per cent to 2,640 yen today, underperforming the Tokyo Stock Exchange’s pharmaceutical sector sub-index which fell 1.3 per cent.

Roche said it continued to monitor the safety of the drug and reported any adverse events to regulatory authorities.

“Tamiflu has been shown in clinical studies and in routine clinical use to have a good safety profile. Tamiflu has been used by over 30 million people worldwide,” Roche said.

Analysts played down the concerns.

“We have not seen these side effects before,” LODH analyst Karl-Heinz Koch said. “Any kind of treatment could lead to mood disorders and therefore be linked to suicidal thoughts. But this is very difficult to establish.”

“This appears to be a panic reaction by Chugai investors where no direct link has been associated with Tamiflu,” Pictet analyst Andrew Fellows wrote in a research note.

The Mainichi newspaper and Kyodo News agency reported on Saturday that a 17-year-old high school student jumped in front of a truck in February last year shortly after taking the medicine, while a junior high school student is believed to have fallen from the ninth floor of his apartment building this February.

“We reported these cases to the health ministry as a link between the deaths and the drug could not be ruled out,” a Chugai spokesman said.

The reports were made separately after each incident, he said.