What is omalizumab? How does it work (mechanism of action)?

Omalizumab is an injectable drug that is used for treating asthma. Omalizumab is a protein that resembles one type of human antibody. Antibodies are proteins produced by the body that recognize foreign substances such as bacteria (that cause infection) and pollens (that cause allergies). Once they recognize a foreign substance, the antibodies attach to receptors on two types of cells in tissues and blood, mast cells and basophils. These cells then release chemicals that cause an allergic reaction that leads to inflammation. Omalizumab blocks the receptors on the surfaces of the mast cells and basophils to which antibodies attach, thereby preventing antibodies from attaching to the cells. As a result, the cells do not release their chemicals, and the allergic reaction and inflammation are prevented. In asthmatic individuals, allergic reactions often cause attacks of asthma. Omalizumab reduces the attacks of asthma by preventing the allergic reactions caused by foreign substances.

  • Omalizumab was approved by the FDA in June 2003.
  • The brand name for omalizumab is Xolair.
  • Omalizumab is available in generic for sterile powder injection; 5 ml vial (150 mg).

What is omalizumab used for?

Omalizumab is a sterile injectable drug used for the treatment of asthma. 

What are the side effects of omalizumab?

The most common side effects observed in patients treated with omalizumab are: 

Use of omalizumab may also lead to serious, life-threatening allergic reactions (anaphylaxis) which manifest as bronchospasm with difficulty breathing, fainting, low blood pressure, and swelling of the tongue or throat.

It is recommended that patients be observed for these reactions for at least two hours after injection of omalizumab; however, these reactions can occur up to 24 hours or longer after the injections, and they have occurred even after one year of regular treatment. Since allergic reactions can occur after any dose, patients should carry medications for emergency self-treatment. In clinical trials cancer occurred more frequently in patients who took omalizumab.


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What is the dosage for omalizumab?

Omalizumab is injected under the skin. The recommended dose is 150-375 mg every 2 to 4 weeks. The dose and frequency is based on body weight and levels of serum IgE, a type of antibody that is important in promoting some types of allergic reactions. Doses greater than 150 mg should be divided and administered at different sites so that no more than 150 mg is administered at each injection site.

Which drugs or supplements interact with omalizumab?

Drug interaction studies have not been conducted with omalizumab.

Is omalizumab safe to take if I'm pregnant or breastfeeding?

Omalizumab has not been adequately studied in pregnant women.

Use of omalizumab by nursing mothers has not been adequately evaluated. Since antibodies similar to omalizumab are excreted in human breast milk, it is likely that omalizumab also is excreted in breast milk.

What else should you know about omalizumab?

How should I keep omalizumab stored?

Omalizumab should be refrigerated between 2 C to 8 C (36 F to 46 F). When mixed with sterile water, the solution should be used within 8 hours if refrigerated between 2 C to 8 C (36 F to 46 F) or within 4 hours if stored at room temperature.


Omalizumab (Xolair) is a drug prescribed for the treatment of asthma that is not adequately controlled with inhaled steroids. Xolair is an injectable drug. Side effects, drug interactions, and patient warnings should be reviewed prior to taking this medication.

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See more info: omalizumab on RxList
Medically reviewed by John P. Cunha, DO, FACOEP

FDA Prescribing Information.