The Muliple Sclerosis (MS) drug Tysabri (natalizumab) has been linked to at least 395 cases of progressive multifocal leukoencephalopathy (PML), a devastating brain infection that usually causes permanent disability or death. Biogen Idec Inc. is now facing at least six Tysabri lawsuits from people who allege that they were not adequately warned that the risk of PML increases with longer Tysabri treatment.
FDA Safety Warnings for Tysabri and PML
- January 20, 2012 — Tysabri PML Warning — FDA recommends that Tysabri patients should undergo blood tests to check for anti-JC virus antibodies. A positive test indicates an increased risk of PML.
- April 22, 2011 — Tysabri PML Warning — FDA warns that PML risk increases with Tysabri treatment longer than two years.
- February 5, 2010 — Tysabri PML Warning — FDA reports 31 confirmed cases of PML in Tysabri patients.
What is Progressive Multifocal Leukoencephalopathy (PML)?
Progressive Multifocal Leukoencephalopathy (PML) is a rare but severe brain infection that causes permanent disability or death. PML is caused by the JC virus, which infects 70-90% of people but only causes infections in people with weak immune systems or those on immunosuppressant drugs, such as Tysabri. PML damages myelin, which is the insulation around neurons, and causes progressive brain damage. The disease is fatal in 50-60% of cases, and there is no cure.
Risk-Factors for Tysabri and PML Infection
Researchers estimate that 11 out of 1,000 people who have all three risk-factors will develop PML on Tysabri:
- Using Tysabri for at least two years.
- History of immunosuppressant drugs, such as mitoxantrone, azathioprine, methotrexate, cyclophosphamide, or mycophenolate mofetil. These drugs are often used to treat people with cancer, organ transplants, or HIV/AIDS.
- Positive blood test for anti-JC virus antibodies.
Symptoms of Tysabri PML Infection
The symptoms of PML typically worsen and change over the course of a few weeks or months. Although symptoms vary depending on the part of the brain involved in the infection, they may include:
- Muscle weakness that gets worse
- Vision problems or blindness
- Speech impairment
- Personality changes
Resources & Additional Info
- Progressive Multifocal Leukoencephalopathy (PML) — National Institute of Health (NIH)
- Tysabri Safety Information — National Multiple Sclerosis (MS) Society
- Tysabri Medication Guide — Biogen Idec, Inc.