Tysabri Brain Infection Risk Updated on Drug Label

The label information on the multiple sclerosis drug Tysabri is being updated to reflect new data on the risk of a serious, and sometimes deadly, brain infection that has killed at least 21 patients using the drug. 

New label data will indicate side effects of Tysabri may lead to as many as 1.5 patients out of every 1,000 contracting progressive multifocal leukoencephalopathy (PML); an aggressive brain infection that is likely connected to the Tysabri’s immune system suppression. The FDA intends to release a drug safety communication on the updated label data in the near future.

A temporary Tysabri recall was issued in 2005 after three users developed PML, a rare and life-threatening brain infection, which attacks the central nervous system, damaging and inflaming the white matter areas of the brain. The drug was reintroduced in July 2006 with stronger warnings about the potential risk of a PML brain infection from Tysabri and the drug was only made available under strict usage guidelines.

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Since Tysabri has been reintroduced there have been 102 PML infections reported; 21 of those resulting in the death of the patient. However, the FDA has felt the drug’s health benefits justify the potential risk.

The label changes will include a table detailing the PML rate of incidence. Patients taking the drug in the first two years only have a 0.3 out of 1,000 chance of developing PML. But the PML rate peaks during the second and third year on the drug to 1.5 incidents per 1,000 patients, before dropping down to 0.9 cases for every 1,000 patients in the third and fourth years of use.

Tysabri (natalizumab) is an intravenous injection given every 28 days to treat multiple sclerosis (MS) and Crohn’s disease. Manufactured by Biogen Idec Inc. and marketed with Elan Corp PLC, Tysabri has been shown to prevent relapse, cognitive decline and vision loss associated with MS. Sales of Tysabri bring in about $1 billion annually.

PML is believed to be caused by the common JC virus, and Tysabri may reduce the ability of the immune system to combat the virus.

In 2009, reports of PML brain infections from Raptiva, a psoriasis drug marketed by Genentech, Inc., led to that drug being removed from the market. Unlike Tysabri, which has remained available with strong warnings for consumers, it was determined that the risk of Raptiva brain infection side effects outweighed the benefits provided in treating psoriasis.


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