Biogen Idec, Elan seek to update Tysabri label regading PML risk

Biogen Idec and Elan announced Wednesday the submission of regulatory filings in both the US and Europe requesting an update to the label of Tysabri (natalizumab) to "include anti-JC virus antibody status as one potential factor to help stratify the risk of progressive multifocal leukoencephalopathy (PML)" in patients taking the multiple sclerosis therapy.

Separately, the companies are developing a blood test that can detect the presence of an antibody to the JC virus, which causes PML. The test is being studied in clinical trials, explained Biogen Idec spokeswoman Kate Weiss. In February, the FDA updated the product's label to add a warning that patients taking Tysabri increase their risk of developing PML as the number of infusions of the drug increases.

Last week, Biogen Idec reported four more cases of PML among patients taking Tysabri, bringing the total number of confirmed cases as of December 2 to 79, with 16 deaths. The company also indicated that the rate of PML cases per 1000 patients had increased slightly to 1.0 from 0.96, which they said was likely explained by the higher number of patients using the therapy for more than two years.

The drug generated $1.1 billion in sales last year.

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