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Available by prescription only, Tysabri is used to prevent worsening of relapses and disabilities caused by multiple sclerosis, and to treat and prevent symptoms of Crohn's disease. It comes in the form of an intravenous (IV) injection that is administered by a healthcare provider once every four weeks. Potential side effects may include nausea, headaches, and fatigue.

What Is Tysabri?

Tysabri® (natalizumab) is a prescription medication that belongs to a group of medicines called immunomodulators. It is approved to:
  • Slow down the worsening of disability and reduce the number of relapses (times when symptoms flare up) in people with multiple sclerosis (MS)
  • Treat and prevent symptoms in people with Crohn's disease.
Whether it is used for MS or Crohn's disease, Tysabri is reserved for people who have not responded to or cannot take other medications to treat their condition.
(Click Tysabri Uses for more information on this topic, including possible off-label uses.)

Who Makes This Medication?

Tysabri is manufactured by Biogen Idec, Inc., for Elan Pharmaceuticals, Inc.

How Does Tysabri Work?

An antibody (also known as an immunoglobulin) is a protein made by the immune system. Antibodies bind to substances in the body called antigens. Tysabri is an anti-alpha-4-integrin antibody. This means it binds to and blocks alpha-4-integrin.
Apha-4-integrins are molecules found on most white blood cells (immune cells). They help white blood cells bind to other cells. When white blood cells bind to certain other cells in blood vessels near the brain, the white blood cells can get into the brain, where they can damage myelin. When white blood cells bind to certain cells in the gastrointestinal tract, they may cause inflammation.
The exact way Tysabri works for MS and Crohn's disease is not entirely known. It is believed that by blocking alpha-4-integrin, Tysabri prevents white blood cells from binding to other cells. This prevents white blood cells from getting into the brain and attacking nerves, which can help with MS, and from causing inflammation in the gastrointestinal tract, which can help with Crohn's disease.
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Tysabri Medication Information

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