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Health Canada Probes Relenza Side Effects

Apr 9, 2008 | Parker Waichman Alonso LLP

Health Canada is looking into reports that Relenza, a drug used to treat the flu, has been linked to deaths and abnormal behavior in children.  In November 2007, a US Food & Drug Administration (FDA) advisory panel had recommended stronger warnings about psychiatric side effects be added to the labeling of Relenza and another anti-flu drug, Tamiflu.  Those warnings were added to the labeling of Relenza earlier in March, while the Tamiflu label was updated in February.

The FDA advisory panel recommendations where based on a review of nearly 600 psychiatric adverse event reports in Tamiflu patients, and another 115 reports among people taking Relenza.  Documents posted online by FDA staffers prior to the meeting said that there have been reports of 596 neuropsychiatric events, including 16 neuropsychiatric-related deaths, among children and adults taking Tamiflu. Among those reports, 75% came from Japan. In total, the FDA said, there were 25 deaths from all causes reported among Tamiflu users on a world-wide basis in patients younger than 21.  Japan was also the origin of 81 of the Relenza reports, but no deaths where associated with that drug. Of the 48 million people treated with Tamiflu since its approval in 1999, the majority of users – 35 million – have been in Japan.

Health Canada updated Tamiflu's safety label after reports of bizarre behavior among patients who took the drug last year.  The new Canadian investigation into Relenza was sparked by the FDA action.  According to Health Canada's adverse reaction database, 27 people have reported adverse reactions to Relenza, including one adult who died. One 14-year-old reported nightmares and another six-year-old temporarily lost consciousness.  Another 96 people reported adverse reactions to Tamiflu, including 11 adults who died and nine who reported psychiatric problems.

Canada has stockpiled millions of doses of Tamiflu and  Relenza in case of a pandemic flu outbreak. Relenza can be inhaled to treat influenza in children aged seven years and older. Tamiflu is prescribed for children age one and up, and is an oral medicine taken within 48 hours of onset of flu symptoms. In a pandemic outbreak, Tamiflu and Relenza would be used to treat people ill with flu. If there is no flu vaccine available, Tamiflu could also be taken daily to prevent illness.