Tysabri (natalizumab)

Natalizumab is a treatment option for adults with moderate or severe Crohn’s disease (CD), one of the two main forms of inflammatory bowel disease (IBD). Natalizumab is sold in the United States under the brand name Tysabri. It is a type of biologic therapy called an integrin receptor antagonist.1

It is usually recommended for patients who do not respond well enough (or cannot take) other types of medicines for treating CD, including aminosalicylates, antibiotics, immunosuppressants, or corticosteroids. It is also an option for people who cannot take, or do not experience benefits from, other types of biologic therapies called anti-tumor necrosis factor (anti-TNF) medicines, such as infliximab, adalimumab, or certolizumab pegol.1,3

How does natalizumab work?

Integrin receptor antagonists, such as natalizumab, are biologic therapies that contain special antibodies that are engineered in a laboratory to specifically target cells in the body that are involved in the process of inflammation. The antibody in natalizumab affects the function of specific types of white blood cells that cause inflammation. The antibodies block a protein on the surface of the white blood cells, which keeps the cells from moving out of the blood vessels and into tissues in the body, where they are part of the process that causes inflammation.1,2

People with CD and other inflammatory bowel diseases have symptoms that are caused by having too much inflammation in their digestive tracts. By blocking part of the process that causes inflammation in the body, natalizumab can benefit some people with moderate or severe CD by:1,2

  • Relieving their symptoms
  • Helping the patient to enter remission more quickly
  • Once they enter remission, helping them to stay in it for a longer time

It is recommended that use should be discontinued if not effective after 12 weeks of treatment. The package insert reads that “In CD, discontinue in patients that have not experienced therapeutic benefit by 12 weeks of induction therapy, and in patients that cannot discontinue chronic concomitant steroids within six months of starting therapy."

Who can take natalizumab?

Natalizumab is approved in the United States to treat adults with moderate-to-severe CD. Before prescribing natalizumab, healthcare providers need to know about any other medicines or supplements that a patient is taking, especially any that affect the way the immune system works. Tysabri may not be used with immunsupressents or TNF inhibitors when used for CD. It is important for women who are pregnant, planning to become pregnant, or breastfeeding to let their healthcare providers know that as well. Healthcare providers also need to know if the patient has any fever or infection, or if they have an medical condition that affects the immune system, such as HIV, AIDS, leukemia, lymphoma, or an organ transplant. This is because natalizumab lowers the body’s immune system response and ability to fight infections, which can be dangerous if the person’s immune system is already affected by one of those conditions.1-3

The way that natalizumab works affects a person’s entire body and weakens the person’s immune system. Taking natalizumab, especially for more than two years, can increase a person’s chances of getting a very rare infection in the brain called progressive multifocal leukoencephalopathy (PML). To note: PML is a black box warning. Because of this risk, the medication is only available through a restricted distribution program. This infection can be very dangerous, and is caused by a virus called the John Cunningham virus. People who already have PML cannot take natalizumab, and everyone who starts treatment with the medication will have a test for that virus.1-3

What side effects are linked to treatment with natalizumab?

The most common side effects that are reported by people who are taking natalizumab include:3

  • Headache
  • Lung infection
  • Vaginitis
  • Stomach area pain
  • Feeling tired
  • Depression
  • Rash
  • Urinary tract infection
  • Pain in your arm and legs
  • Nose and throat infections
  • Joint pain
  • Diarrhea
  • Nausea

These are not all the possible side effects of natalizumab. Patients should talk to their doctor about what to expect with treatment with natalizumab. Patients should contact their healthcare providers right away if they start to experience any symptoms that last more than a couple of days. This is especially important if the following signs of PML, which are problems with:3

  • Thinking
  • Eyesight
  • Strength
  • Balance
  • Weakness on one side of the body
  • Trouble using arms and legs

Because of the way that natalizumab works, there are serious conditions other than PML that it can cause in a small number of patients. Healthcare providers will monitor patients for any signs of the following conditions:3

  • Herpes encephalitis and meningitis
  • Liver damage
  • Infections
  • Allergic reactions to the medication
  • Thrombocytopenia

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Written by: Anna Nicholson and Emily Downward | Last Reviewed: April 2022