Tysabri (natalizumab) is associated with hundreds of cases of Progressive Multifocal Leukoencephalopathy (PML), which is a life-threatening brain infection caused by the JC virus.
UPDATE: At least 6 Tysabri PML Lawsuits Filed Against Biogen Idec, Inc.
September 18, 2013 — The FDA has received 395 reports of PML in Tysabri patients, including 92 deaths. At least six people who had PML after using Tysabri have filed lawsuits alleging that Biogen Idec Inc. did not warn about the risk. Click here to read more.
FDA Drug Safety Communication
The U.S. Food and Drug Administration issued a Drug Safety Communication after it approved a blood test that could identify whether a person had a latent JC virus. The blood test looks for antibodies to the virus. The blood test was developed by the drug-company that produces Tysabri, which had been linked to Progressive Multifocal Leukoencephalopathy (PML).
What is Progressive Multifocal Leukoencephalopathy (PML)? PML is an incurable, deadly brain infection. It almost always occurs in people with weakened immune-systems, or people taking immunosuppressant medications, such as Tysabri. The infection can be caused by the John Cunningham (JC) virus, which is thought to be latent in 40-80% of the adult U.S. population. Usually, the JC virus is harmless. When this virus is reactivated, however, it attacks a part of the brain called the “myelin”, which is a layer of fatty tissue and protein that insulates nerve cells in the white matter. When the myelin is damaged, a person suffers severe, disabling, and permanent damage to their central nervous system. There is no known way to prevent PML caused by this virus, and when a person develops an infection, there is no cure.
Tysabri has been linked to an increased risk of PML for many years. The medication was pulled off the market in 2005, and reintroduced in 2006 with a black-box warning. Because the drug-company knew that the JC virus was responsible for PML, they decided to invest in research to identify patients who had the virus. Patients with the virus could be counseled that they were at high-risk of developing PML, and patients without the virus would know that they had a lower risk.
On January 20, 2012, the FDA approved a diagnostic blood test that could screen for people with a latent JC virus. The test is called the stratify JCV Antibody ELISA test.
The FDA will also be updating the safety labeling to include information about the risk factors that increase a patient’s chances of developing PML.
Risk Factors for PML
The FDA has found three major risk factors that increase a patient’s chance of developing PML. When a patient has all three risk factors, their estimated chance of developing PML is 11 per 1,000 patients.
The risk factors are as follows:
- The presence of anti-JC virus antibodies, which can now be tested for using a blood test
- Longer Tysabri treatment, especially more than 2 years.
- Prior treatment with an immunosuppressant medication (for example: mitoxantrone, azathioprine, methotrexate, cyclophosphamide, or mycophenolate mofetil)
Tysabri (natalizumab) is a pharmaceutical drug most often used in the treatment of two diseases: multiple sclerosis and Crohn’s disease. Tysabri is an “immunomodulator” medication, which means that it prevents certain cells in the immune system from reaching a patient’s nerves and spinal cord, where they would otherwise cause damage.
Multiple sclerosis (MS) is a degenerative disease in which the immune system attacks the nerves in a person’s body. Over time, MS may gradually case weakness, numbness, loss of motor coordination, incontinence, and impaired speech and vision. Tysabri is given to MS patients who have recurrent episodes, or “flare-up” symptoms. It is used to slow down the worsening symptoms that cause disability.
Crohn’s Disease is a condition in which the immune system over-reacts, and can’t tell the difference between healthy tissue and foreign substances. Immune cells attack the lining of a person’s intestinal tract, causing chronic inflammation. It may affect the upper intestine, lower intestine, mouth, or rectum, and causes pain, diarrhea, unintentional weight-loss, and fever. Tysabri inhibits this over-active immune response.