Tysabri (natalizumab)

Tysabri® is an injectable prescription medication used to treat adults with relapsing forms of multiple sclerosis (MS). Tysabri is a disease-modifying treatment (DMT), which can slow the progression of MS and reduce the number of relapses, or exacerbations.

Tysabri increases the risk of developing a rare brain infection known as progressive multifocal leukoencephalopathy (PML). PML is an opportunistic viral infection of the brain that has no known treatment, prevention, or cure. PML frequently leads to severe disability or death. Because of the risk of PML, Tysabri is only used in patients for whom the expected benefit outweighs this risk.

What is the ingredient in Tysabri?

The active ingredient in Tysabri is natalizumab, a monoclonal antibody that binds to certain white blood cells.

How does Tysabri work?

While the exact way Tysabri works isn’t fully understood, researchers believe that it binds to a particular integrin receptor on the surface of certain white blood cells (all leukocytes except neutrophils). Blocking this receptor on the white blood cells may stop them from crossing into the central nervous system (brain, spinal cord and optic nerve) and reduce the inflammation in the brain that is overactive in MS.

What are the possible side effects of Tysabri?

The most serious side effect of Tysabri is the risk of PML, the viral brain infection that can lead to significant disability or death. The risk of PML is increased with a longer duration of using Tysabri (especially longer than two years), prior use of medications that suppress the immune system (immunosuppressants), and a previous infection of the John Cunningham Virus. While taking Tysabri and for 6 months after treatment, people who experience any of the following symptoms should report them immediately to their healthcare professional:

  • Any new or worsening medical problems such as difficulty with thinking, eyesight, balance, or strength
  • Weakness on one side of the body
  • Difficulty using arms or legs

The most common side effects experienced in people with MS receiving Tysabri in clinical trials included:

  • Headache
  • Fatigue
  • Joint pain
  • Urinary tract infection
  • Lower respiratory tract infection
  • Stomach pain or nausea
  • Vaginal infection
  • Depression
  • Pain in the arms or legs
  • Abdominal pain or discomfort
  • Diarrhea
  • Rash

Tysabri may also cause other serious side effects, including:

  • Increased risk of herpes infections, which may cause blindness, brain or spinal cord infection, and may lead to death
  • Liver damage, which may appear as yellowing of the skin or eyes, darkening of the urine, nausea, fatigue, vomiting, and may lead to liver failure requiring a liver transplant
  • Serious allergic reactions, which can cause hives, itching, or difficulty breathing
  • Weakened immune system, which could increase the risk of getting infections
  • Thrombocytopenia, or low levels of platelets in the blood

These are not all the possible side effects of Tysabri. Patients should talk to their doctor about what to expect with treatment with Tysabri.

Things to know about Tysabri

Because Tysabri can weaken the immune system, it is important for patients to tell their doctor about all their medical conditions, particularly any conditions that weaken the immune system, including human immunodeficiency virus (HIV) infection, acquired immune deficiency syndrome (AIDS), a previous organ transplant, leukemia, or lymphoma.

Tysabri should not be used by women who are pregnant, breastfeeding, or those who plan to become pregnant or breastfeed. It is not known whether Tysabri may harm a child through breastmilk or the placenta. Tysabri has been detected in human milk.

Before starting Tysabri, patients should talk to their doctor about all medications, vitamins, and supplements they are taking, especially any medications that can weaken the immune system.

People who have PML or who are allergic to Tysabri should not take Tysabri.

For more information, read the full prescribing information for Tysabri.

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Written by Emily Downward | Last review date: July 2021.