Tysabri
Tysabri (natalizumab) is a medication used to treat multiple sclerosis (MS) and Crohn's disease. As of February, 2010, Biogen Idec Inc. had disclosed 35 cases of progressive multifocal leukoencephalopathy (PML) in MS patients taking Tysabri. So far, eight of the 35 patients who contracted PML have died from the disease. PML is a rare brain infection that is usually fatal.
Tysabri Pulled From the Market Before
Tysabri was approved by the Food and Drug Administration in November, 2004. When patients involved in clinical trials of the drug began developing PML the FDA pulled it. Tysabri had only been on the market for three months.
The FDA allowed Tysabri to be sold again in 2006. It is only the second drug ever that the FDA has pulled for safety reasons and then allowed back on the market. The reintroduction came with heavy restrictions.
Long Term Use of Tysabri Increases Risk
The FDA issued a new warning to doctors and patients in February, 2010. The warning label on the drug was actually changed by the manufacturer in November, 2009. The new warning says that long-term use increases the risk of developing PML.
How Tysabri Works in MS
MS is an autoimmune disease. In MS your own immune system attacks your brain and spinal cord (central nervous system). It damages the protective covering (myelin) of nerve cells destroying their ability to communicate. The areas of damage are called lesions.
Tysabi is thought to work by blocking the immune system's attack on the brain, by keeping white blood cells from getting into the brain.
Tysabri and PML
In order to stop or slow the damage to the brain, caused by the immune system, Tysabri inhibits the immune system's ability to work in the brain leaving the brain susceptible to infection.
PML is caused by a common virus called JC virus. It only turns into PML in people with compromised immunes systems. Much like MS itself, PML damages the protective covering of the nerve cells in the white matter of the brain. The result is declining brain function and, eventually, death.
Other Side Effects of Tysabri
PML is the most serious side effect associated with Tysabri use, but certainly not the only one. Other side effects can include:
- Increased risk of serious infections
- Liver damage
- Severe allergic reaction
- Joint pain
- Fatigue
- Headache
- Depression
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