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How does Xolair work?

Medically reviewed by Carmen Fookes, BPharm. Last updated on Jan 19, 2022.

Official answer

  • Xolair works by preventing IgE from binding to IgE receptors on mast cells and basophils.
  • This prevents mast cells and basophils from releasing histamine and heparin.
  • Histamine narrows smooth muscle in the airways making it harder to breathe and also causes tissue swelling, itchy skin, hives, and other allergic-type symptoms.
  • Heparin makes it harder for blood to clot.

Xolair (omalizumab) is an antibody that may be used to treat allergic asthma that is moderate-to-severe, persistent, and not adequately controlled by inhaled corticosteroids, in adults and children aged 6 and over who have had a positive skin test to an allergen or who react to an allergen that is present in their environment year-round.

Xolair is also approved to treat:

  • Urticaria (hives) in adults and children aged 12 and older who have already tried antihistamines without success
  • Nasal polyps in adults aged 18 years and older.

How does Xolair work?

Xolair works by inhibiting the binding of IgE to IgE receptors on mast cells and basophils. Mast cells and basophils are specific cells of the immune system that contain histamine and heparin. As soon as IgE binds to an IgE receptor it causes the release of histamine and heparin from the cell.

Histamine is a chemical that has many inflammatory effects in the body. It contracts the smooth muscle tissue in the lungs, uterus, and stomach; dilates blood vessels causing an increase in permeability and a lowering of blood pressure; stimulates the secretion of gastric acid in the stomach; and speeds up the heart rate. Histamine also causes symptoms such as a runny nose, watery eyes, tissue swelling, itchy skin, and hives.

Because histamine contracts the breathing tubes it can cause wheezing or make it harder to breathe. Histamine is also one of the main chemicals involved in anaphylaxis, a severe and often fatal allergic response to a previously encountered allergen.

Heparin is an anticoagulant that slows the formation of blood clots.

By inhibiting the binding of IgE to the IgE receptor, Xolair prevents the release of histamine and heparin and also reduces the number of IgE receptors on basophils.

IgE levels are increased in people with allergic asthma when they inhale allergens such as pet dander or dust mites which is why Xolair is effective at treating allergic asthma. Xolair will not treat an acute asthma attack or status asthmaticus.

93% of people with moderate-to-severe chronic urticaria have increased total IgE levels.

Xolair is not approved for the treatment of other allergic conditions.

  • Xolair (omalizumab) [Package Insert] Janeway
  • CA Jr, Travers P, Walport M, et al. Immunobiology: The Immune System in Health and Disease. 5th edition. New York: Garland Science; 2001. The production of IgE. Available from:
  • Kessel A, Helou W, Bamberger E, et al. Elevated serum total IgE--a potential marker for severe chronic urticaria. Int Arch Allergy Immunol. 2010;153(3):288-293. doi:10.1159/000314370

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