WASHINGTON -- Federal health advisers are looking into the deaths of 12 Japanese children who took Tamiflu, part of their annual safety review of the anti-flu medication and seven other drugs.
There are no reports of deaths in the United States or Europe associated with Tamiflu.
"Based on the information we have right now, we cannot say definitively there is a causal relation between the drug and the children's death," Dr. Murray Lumpkin, the deputy commissioner of the U.S. Food and Drug Administration, said Thursday.
The Japanese deaths were detailed in papers released in advance of a Food and Drug Administration advisory committee meeting today.
An update by FDA staff also includes reports of 32 "neuropsychiatric events" associated with Tamiflu, all but one experienced by Japanese patients. Those cases included delirium, hallucinations, convulsions and encephalitis.
"Clearly, any time you get a report of a death or a serious occurrence, you want to look into it," Lumpkin said.
The FDA sought and received more information from the Swiss pharmaceutical company Roche Holding AG, which makes Tamiflu, and from Japanese health authorities. It has not issued any warnings or initiated any other action, spokeswoman Susan Bro said.
Lumpkin said "millions and millions" of patients have safely used the drug to treat the flu.
Complicating the issue is that many of the Japanese death and adverse reaction reports list symptoms commonly associated with the flu, he said.
"It is very difficult, when the underlying disease causes what it is being reported, to figure out: Is it the underlying disease? Is it the drug?" said Lumpkin.
Roche said that several studies in the United States and Canada had shown that the death incidence rate of influenza patients who took Tamiflu was far below those who did not.
"The mortality was actually lower versus those who did not receive the drug," said Joseph Hoffman, who heads pharmaceutical development for virology and transplantation at Roche.
Roche has supplied the FDA with two additional studies it commissioned that evaluated the safety of Tamiflu in pediatric patients.
Japan's Health Ministry warned last week that Tamiflu may induce "strange behavior" after reporting that two teenage boys died shortly after taking the medicine.
"Roche has carefully reviewed these events and has concluded that a causal link cannot be established," the company said in a statement released on Monday.
However, the Japanese distributor of the Roche-patented drug told health officials it could not rule out a link between Tamiflu and the deaths.
Roche said the high number of deaths and adverse neuropsychiatric events in Japan was also due to the fact that two of three people taking Tamiflu are in Japan. Of 32 million people treated with Tamiflu since its approval in 1999, 24 million were in Japan.
The U.S. labeling for Tamiflu lists nausea and vomiting as its most serious side effects. Its labeling in Japan includes any adverse effects that have been reported -- including impaired consciousness, abnormal behavior and hallucinations -- regardless of whether they can be attributed to the drug, according to Roche.
Tamiflu is one of the few drugs believed effective in treating bird flu, which health officials fear could spark a pandemic should it mutate into a form easily passed from human to human.