Published: 2 December 2021


Consider thromboembolic events in patients given omalizumab

Published: 2 December 2021
Prescriber Update 42(4): 56–57
December 2021

Key messages

  • Omalizumab is a monoclonal antibody indicated for the treatment of allergic asthma and chronic idiopathic urticaria.
  • Thromboembolic events have been observed in patients being treated with omalizumab.

Thromboembolic events associated with omalizumab treatment (brand name Xolair) have been observed in clinical trials and reported in the post-marketing setting, including in New Zealand. The Health and Disability Commissioner recently reported on a case where the patient had been treated with omalizumab and experienced fatal ischaemic bowel.


Omalizumab is a recombinant monoclonal antibody that selectively binds to free but not receptor-bound human immunoglobulin E (IgE).1,2 IgE plays an important role in many diseases such as allergic asthma and chronic idiopathic urticaria.3 Omalizumab blocks acute IgE-mediated responses to inhaled and ingested allergens and late-phase responses to inhaled allergens.2

Xolair is approved for the treatment of allergic asthma and chronic idiopathic urticaria.1

Thromboembolic events

The Xolair data sheet states that a higher rate of arterial thromboembolic events in Xolair-treated patients has been shown in studies compared with control patients.1 Arterial thromboembolic events included stroke, transient ischemic attack, myocardial infarction, unstable angina and cardiovascular death.1

A review of safety studies by the United States Food and Drug Administration suggested a slightly increased risk of adverse reactions involving the heart and blood vessels supplying the brain in patients being treated with omalizumab.4 The United Kingdom’s Medicines and Healthcare products Regulatory Agency also highlighted a potential risk of thrombotic adverse reactions with omalizumab; however, the finding was not statistically significant at the 95 percent level.5

Prescribers should be observant of thromboembolic events in patients being treated with omalizumab.

Refer to the Xolair data sheet and the Health and Disability Commissioner’s report on the case mentioned above for more information.


  1. Novartis New Zealand Limited. 2021. Xolair New Zealand Data Sheet 13 May 2021. URL: (accessed 21 September 2021).
  2. Oettgen HC. 2016. Fifty years later: Emerging functions of IgE antibodies in host defense, immune regulation, and allergic diseases. Journal of Allergy and Clinical Immunology 137(6): 1631–45. DOI: 10.1016/j.jaci.2016.04.009 (accessed 18 October 2021).
  3. Stokes J, Casale TB. 2020. The biology of IgE. In: UpToDate 8 October 2020. URL: (accessed 18 October 2021).
  4. US Food and Drug Administration. 2014. FDA Drug Safety Communication: FDA approves label changes for asthma drug Xolair (omalizumab), including describing slightly higher risk of heart and brain adverse events 26 September 2014. URL: (accessed 18 October 2021).
  5. Medicines and Healthcare products Regulatory Agency. 2011. Omalizumab: potential risk of arterial thrombotic events. Drug Safety Update 4(7): A4 [published online 11 December 2014]. URL: (accessed 18 October 2021).
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