FDA amends label of Biogen Idec's Tecfidera to warn of a case of PML

The FDA on Tuesday updated the label of Biogen Idec's multiple sclerosis therapy Tecfidera (dimethyl fumarate) to describe a case of fatal progressive multifocal leukoencephalopathy (PML) in a patient who used the drug. The agency noted that the patient had an extremely low leukocyte count prior to developing PML.

Biogen Idec previously disclosed the patient's death while announcing its third-quarter earnings, noting that the patient used Tecfidera for more than four years and experienced low blood cell counts for most of the treatment course. The FDA said that the patient was not using any other medicines that affect the immune system or treatments believed to be associated with PML. The regulator, which had recommended that doctors monitor patients' white blood cell counts during treatment with the MS drug, added that this is the only confirmed case of PML in patients treated with Tecfidera.

The therapy, which was cleared by the FDA in March 2013, generated $787 million in revenue for the quarter ended September 30. Analysts previously suggested that the case of PML was not a major concern, as 100 000 patients have been treated with the drug without developing the rare disease. For further analysis see ViewPoints: Biogen Idec's disappointing earnings – storm clouds brewing or unrealistic expectations?

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