Risk of PML with Tysabri use, warns FDA

The announcement read, “The U.S. Food and Drug Administration is alerting the public that the risk of developing progressive multifocal leukoencephalopathy a rare but serious brain infection associated with the use of Tysabri (natalizumab), increases with the number of Tysabri infusions received.”

FDA made the safety announcement regarding the drug via their website on Friday after getting reports of 31 confirmed cases of PML in patients treated with Tysabri since July 2006 to Jan. 21, 2010.

Also, out of these 31 patients using the drug for treating multiple sclerosis (MS), eight have died because of the rare PML infection.

The report
According to the report titled ‘FDA Drug Safety Communication: Risk of Progressive Multifocal Leukoencephalopathy (PML) with the use of Tysabri (natalizumab)’, PML threat rises with the number of Tysabri infusions received.

“The overall worldwide cumulative rate of PML in patients who have received at least 24 infusions is 1.3 cases of PML per 1,000 patients. In the U.S., the cumulative rate of PML in patients who have received at least 24 infusions is 0.8 per 1,000 patients,” the FDA reports.

It adds, “Outside of the U.S., the cumulative rate of PML in patients who have received at least 24 infusions is 1.9 per 1,000 patients.”

What is PML?
PML is an infrequent contamination of the brain caused by the JC virus, a common virus often acquired during infancy.

The warning signs of PML may include trouble in walking and other movements, decline in mental function, and problems with vision and speaking. Headaches and seizures may also occur due to PML.

Tysabri fact file
Tysabri is usually suggested for patients who are unable to stand any other multiple sclerosis therapy. In January 2008, it was also permitted for patients with Crohn's disease (CD) in the U.S.

The immunosuppressant drug was approved by the FDA in 2004, and in 2005, the makers of the drug suspended it after reports of development of PML in three multiple sclerosis patients.

It re-emerged in the markets for curing patients with relapsing forms of MS in June 2006.

Drug label carries FDA’s warning
The label of the drug contains a warning that the risk of a rare brain infection called progressive multifocal leukoencephalopathy increases with longer use of Tysabri, according to the posting by the Food and Drug Administration.

Cambridge based, Biogen Idec’s spokeswoman, Naomi Aoki says, “The new label went into use in November in the United States and in January in Europe after company officials approached regulators on both continents about modifying the label to reflect the risks of long-term use.”