Review of Tysabri in Multiple Sclerosis

Safety and What to Watch Out for When Taking Tysabri

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Tysabri is for people with relapsing forms of MS and is administered as an infusion (given through your vein) once every 28 days. It's generally prescribed for patients who do not respond to other MS disease-modifying therapies (meaning their disease continues to worsen) or who were unable to tolerate other MS therapies, usually from harmful or bothersome side effects.

Risk of PML with Tysabri

The most serious (but rarest) risk of taking Tysabri is PML (progressive multifocal leukoencephalopathy), which is a potentially fatal brain infection caused by the JC virus.

People are at a higher risk of getting PML if they are taking other medications that weaken their immune system while taking Tysabri. Two other risk factors that increase a person's chance of developing PML include taking Tysabri for more than two years and/or testing positive for the JC virus antibody.

A person with none of these three risk factors has about a 1/50,000 chance of developing PML while on Tysabri. But if all three risk factors are present, the risk is about 11-13/1000. If a person just tests positive for the JC virus antibody (no other risk factors) their risk of developing PML is about 1/1000.

To determine a person's risk of developing PML, doctors will check a blood test for the antibody to the JC virus prior to prescribing Tysabri and every six months while the person is taking Tysabri. Based on the results, a doctor will review the risk/benefit ratio of taking Tysabri with the patient.

 In addition, doctors will obtain an MRI (to distinguish future MS symptoms from possible future PML symptoms) prior to starting Tysabri.

Monitoring for PML as a Patient on Tysabri

As a patient, if you do take Tysabri, it's critical to contact your doctor right away if you develop any symptoms that are concerning for PML.

This can be tricky as many PML symptoms mimic those of MS. Examples of PML symptoms include: 

  • gradual weakness on one side of the body
  • clumsiness
  • vision changes
  • personality changes
  • problems with thinking, memory, and orientation leading to confusion

Other Potential Side Effects and Warnings of Tysabri

Common side effects of Tysabri include

Tysabri can also cause liver damage, which can be detected by blood tests. Signs and symptoms of liver injury include yellowing of the skin and eyes, significant fatigue, nausea and vomiting, or dark urine.

Tysabri too can cause herpes infection of the brain, spinal cord, and meninges. Signs and symptoms of this include fever, headache, neck stiffness, vision problems, confusion, and behavior changes. 

There have been cases of severe allergic reactions in patients undergoing Tysabri, some requiring treatment (even hospitalization).

The symptoms of this include hives/itching, chills, dizziness, chest pain, flushing, trouble breathing and low blood pressure.

In addition, people on Tysabri may be more susceptible to infections, and should take measures to avoid them, including good hand washing habits and avoiding people who are sick, when possible.

Monitoring While on Tysabri

Tysabri can only be given at an infusion center that is registered through the "TOUCH" program. "TOUCH" stands for "Tysabri Outreach: Unified Commitment to Health" and is the program that was put in place in an attempt to catch any potential cases of PML in early stages, as well as prevent them.  

Pregnancy on Tysabri

Tysabri is considered to be "pregnancy category C," meaning that it caused some harm to fetuses in animal studies, but the effect in humans is unknown. Tysabri should not be used by women who are pregnant and should be stopped for some time before trying to conceive (discuss this with your doctor). 

Bottom Line

You will have to work closely with your doctor to decide if Tysabri is the right medication for you. If you do decide to take it, be sure to read the medication label in detail. Also, be sure you discuss the signs and symptoms of PML, infection, liver damage, and an allergic reaction with your doctor. Ensure you have proper followup too (e.g. 3 months after the first infusion), and that all your other doctors know you are taking Tysabri. 


Krumbholz, M., et al. (2007). Delayed Allergic Reaction to Natalizumab Associated With Early Formation of Neutralizing Antibodies. Archives of Neurology, 64:1331-1333.

Polman, C.H., et al. (2008). A randomized, placebo-controlled trial of natalizumab for relapsing multiple sclerosis. New England Journal of Medicine, Mar 2;354(9):899-910.

National MS Society. (2016). The MS Disease-Modifying Medications

Rudick, R.A., et al. (2006). Natalizumab plus interferon beta-1a for relapsing multiple sclerosis. New England Journal of Medicine, Mar 2;354(9):911-23.

U.S. Food and Drug Administration. Tysabri.

DISCLAIMER: The information in this site is for educational purposes only. It should not be used as a substitute for personal care by a licensed physician. Please see your doctor for diagnosis and treatment of any concerning symptoms or medical condition.

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