FDA issues warning over safety of Tysabri use

ROCKVILLE, Md. Patients using a drug for treating multiple sclerosis may be at increased risk of developing a deadly brain infection, the Food and Drug Administration said Friday in a warning to healthcare professionals and patients.

The FDA said that 31 patients using the drug Tysabri (natalizumab), marketed by Elan Corp. and Biogen Idec, had developed progressive multifocal leukoencephalopathy, or PML, as of Jan. 21. The drug’s safety labeling has been updated to reflect the risk. Still, the agency said the benefits of the drug outweigh the potential risks.

PML is caused by the JC virus, a virus that occurs naturally in most adults but is kept in check by the body’s immune system. When the immune system becomes compromised due to diseases such as AIDS or the use of immune-suppressing drugs, the risk that the virus will multiply and cause irreversible and fatal damage to the brain increases.

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