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How long before Xolair starts working?

Medically reviewed by Carmen Fookes, BPharm. Last updated on Dec 10, 2020.

Official answer

  • Free serum IgE levels are decreased within an hour of Xolair administration.
  • However it may take several months for the full effects of Xolair to be seen, although some symptom improvement may be noted after a few weeks.
  • Trials using Xolair in people with allergic asthma noted significant improvements after 4 months.
  • Trials using Xolair in people with chronic urticaria noted significant improvements after 3 months.
  • Xolair is given every two to four weeks and it can take approximately 7 to 8 days for peak concentrations to be reached after a single injection.
  • Once discontinued, Xolair may persist in the body for 6 months to one year.

Xolair (omalizumab) is an antibody that may be used to treat allergic asthma that is:

  • Moderate-to-severe
  • Persistent
  • 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.

Xolair is administered by injection under the skin (subcutaneously) once every two to four weeks. The dosage of Xolair is based on body weight. Xolair is absorbed slowly, with peak concentrations being reached approximately 7 to 8 days after administration.

Although some improvement in symptoms may be noted after a few weeks, it may take several months for Xolair to start working properly in your body. Significant improvements have been noted in trials in asthma patients of four months duration and in trials of people with urticaria of three months duration.

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.

Xolair forms stable Xolair/IgE complexes which are more slowly excreted from the body than free IgE. This means that total serum IgE levels (bound and unbound) will show an increase in laboratory testing; however, serum-free IgE levels are decreased within an hour of injection, and decreases of greater than 96% have been reported.

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.


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