More than 100 recent cases of delirium, hallucinations and other unusual psychiatric behavior in Japanese patients treated with Tamiflu should have parents watching for similar reactions when treating their children with the flu drug. That's the new advice from the Food and Drug Administration in adding a new precaution to the label of the influenza drug, prescribed about 2 million times a year in the U.S.
The FDA updated the label after receiving the 103 reports of abnormal behavior, most of which involved children in Japan. Japan uses more Tamiflu than any other country in the world, with more than 30 million prescriptions since 2001. It's been prescribed about 8 million times in the U.S. since 1999.
The FDA said a relationship between the drug and the behavior had not been established and that the updated label was "intended to mitigate a potential risk associated with Tamiflu." It recommends that close monitoring of patients begin immediately after starting treatment with the drug.
The changes bring the U.S. label more in line with the Japanese one, which already warned that such abnormal behavior could occur. The previous FDA-approved label mentioned only that "seizure and confusion" had been seen in some patients.
Tamiflu is made by the Swiss pharmaceutical company Roche Holding AG. Roche spokesman Terence Hurley said there was no evidence the drug caused the rarely occurring adverse events. Both Roche and the FDA also said that severe cases of the flu can spark the abnormal behavior flagged in the updated label.
Furthermore, the FDA acknowledged that stopping treatment with Tamiflu could actually harm influenza patients if the virus is the cause of delirium, hallucinations and other abnormal behavior, such as aggression and suicidal thoughts.
Health officials have been sensitive about taking any action that might dissuade people from taking Tamiflu, since the drug could play an important role in an outbreak of bird flu. The drug doesn't prevent flu but can reduce the length and severity of its symptoms.
Previously, Roche has cited studies from the U.S. and Canada that show the death rate of influenza patients who took Tamiflu was far below those who did not. Still, the number of reports of bizarre behavior is increasing.
The 103 new cases occurred between Aug. 29, 2005, and July 6, 2006. The tally marks a sharp increase when compared with the 126 similar cases logged over more than five years between the drug's approval in 1999 and August 2005, the FDA said.
Even though severe cases of the flu can spark abnormal behavior, the number and nature of the newly reported cases — along with comments from doctors who believe the behavior was associated with the drug — keep the FDA from ruling out Tamiflu as the cause, the agency said.
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.
According to the label, Tamiflu is for the treatment of uncomplicated acute illness due to flu in patients 1 year and older who have shown symptoms for no more than two days.