In briefing documents released Tuesday ahead of an FDA advisory panel meeting on October 16, FDA staff suggested that a black box warning concerning potential adverse neuropsychological effects should remain on the label of Pfizer's anti-smoking therapy Chantix (varenicline). The FDA added a black box warning to the drug's label in 2009 following reports that the therapy was associated with severe side effects, including suicidal thoughts, erratic behaviour and drowsiness.
Specifically, agency reviewers expressed "concerns about the validity" of some data submitted by the company, adding that large studies conducted by outside groups provided "evidence of insufficient quality to either rule in or rule out increased risk of suicide." Additionally, FDA staff indicated that the observational studies submitted by Pfizer "had a number of study design limitations," adding that "these limitations may underestimate the actual incidence of neuropsychiatric adverse events ... associated with varenicline."
Meanwhile, FDA reviewers also indicated that any decision regarding removal of the black box warning should not be issued until Pfizer completes a required large-scale study comparing the psychiatric side effects of Chantix and buproprion. Results from the study are anticipated next year.
Reports of psychiatric side effects of Chantix were first reported in 2007, and since then, the FDA noted that it received about 48 200 domestic adverse event reports for the therapy between 2008 and 2013. Additionally, Pfizer has agreed to pay approximately $300 million to settle various lawsuits alleging that Chantix caused untoward side effects, including payments totalling about $273 million to settle 80 percent of outstanding lawsuits in 2012.
Chantix generated sales of $648 million last year, down from peak revenue of $883 million in 2007.
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