TOKYO (Reuters) - Concerns that the influenza drug Tamiflu -- seen as effective against a possible pandemic triggered by bird flu -- may induce fatal side effects are growing in Japan after two people who took it fell to their deaths last month.
The deaths, the latest cases of abnormal behavior by those who took Tamiflu, prompted the Health Ministry to issue a warning last week that influenza patients could show psychiatric problems, although it has denied the drug was responsible for them.
But the move was too little too late, said a group whose members say they are victims of Tamiflu side effects, which came to light in Japan in 2005 after 12 children died and 32 experienced abnormal behavior after taking the drug.
"Had they issued a warning earlier, then the number of deaths could have been halved," said Haruhiko Nokiba, whose 17-year-old son walked onto an expressway shortly after taking Tamiflu and was hit and killed by a truck in 2004.
The incident was seen as a suicide, but Nokiba, who heads the victims and families group, said his son had no reason to kill himself and circumstances showed that it was a result of abnormal behavior.
"He ran out into the snow barefoot in his pajamas, climbed over a 3-meter fence to cross train tracks and then ran into a truck," Nokiba told Reuters in an interview this week.
According to the Health Ministry, 54 people have died so far after taking Tamiflu, and in February, a 14-year-old girl and a boy fell to their deaths from their apartment homes in separate incidents after taking the drug. Neither had left a suicide note.
NO LINK PROVEN
Swiss drug maker Roche Holding AG, which produces Tamiflu, also known generically as oseltamivir, has denied a link between the medication and the deaths, adding that influenza itself could cause psychiatric problems.
"These events are extremely rare in relation to the number of patients treated," Roche spokeswoman Martina Rupp said last week.
"It's very important to state that none of these events were linked to Tamiflu."
Tamiflu has been used to treat 50 million people since it was approved in 1999, and in 2005, there were only 103 reports of neuropsychiatric problems, Rupp added.
Countries around the world are stockpiling the antiviral drug in case of a human influenza pandemic that experts fear could be sparked by the H5N1 bird flu virus.
Chugai Pharmaceutical Co. Ltd., which sells the drug in Japan, added a reference to abnormal behavior as a possible side effect inside Tamiflu's package in 2004, but victims' groups want a stronger warning.
In November, the U.S. Food and Drug Administration decided to require Roche to put a caution on Tamiflu labels urging close monitoring for abnormal behavior, such as delirium, although it said it was unknown if the drug contributed to the psychiatric problems.
A survey of some 2,800 children conducted by a Health Ministry team last year found that there was no evidence of a relationship between Tamiflu and abnormal behavior.
Of those who took the drug, 11.9 percent showed such behavior, while 10.6 percent of patients who did not use the medication also exhibited abnormal behavior, the poll showed.
But Rokuro Hama, a medical doctor who heads a watchdog group on the side effects of drugs, said the ratio of those showing abnormal behavior is four times higher among those who took Tamiflu if limited to the period immediately after taking the drug.
The ministry is carrying out a more thorough survey aiming to poll 10,000 influenza patients and come up with the results later in the year, a ministry official said.
(Additional reporting by Sam Cage in Zurich)