Omalizumab is a humanised monoclonal antibody (biological treatment) that binds to circulating immunoglobulin E (IgE) and reduces the release of inflammatory mediators from mast cells and basophils.
In New Zealand, it is currently (as of 2020) licensed as an add-on therapy for patients with severe, persistent allergic asthma and for patients 12 years of age or older with severe chronic idiopathic (spontaneous) urticaria that remain symptomatic despite H1-antihistamine treatment. It is funded in New Zealand by PHARMAC on Special Authority application under certain circumstances.
It is given by subcutaneous injection in a dose of two 150-mg injections, once every 4 weeks. The patient should remain under observation for a period of time after the injection as a precaution in case of an allergic reaction to it.
The trade name of omalizumab is Xolair™.
What is chronic spontaneous urticaria?
Chronic spontaneous urticaria (also called chronic idiopathic urticaria) is defined as hives or weals that last for at least 6 weeks, with or without angioedema. Urticaria is often extremely itchy, interfering with sleep, daily activities, social interactions, school, and work life.
Symptoms may resolve after a few months; however in about 50% of cases symptoms persist for 3–5 years, and in 20% of cases symptoms can persist for more than 10 years.
Urticaria most often results from the effect of histamine on H1-receptors located on the endothelial cells lining blood vessels. Histamine causes the cells to separate, so that tissue fluid leaks out, forming a weal. Histamine also affects sensory nerves, resulting in a neurogenic erythematous flare and pruritus.
Chronic urticaria may be refractory to antihistamines and associated with a pronounced cellular infiltrate.
What is the role of omalizumab in the treatment of urticaria?
Omalizumab is intended to be used as second-line therapy for the treatment of chronic spontaneous urticaria that is refractory to oral antihistamines. Many patients also fail to respond to a variety of other systemic therapies including systemic steroids and immunomodulating drugs.
See more about key clinical-trial evidence for omalizumab.
How does omalizumab work in urticaria?
Immunoglobulin E (IgE) triggers an allergic reaction (eg, asthma) in response to an allergen (eg, cat dander). Although chronic spontaneous urticaria is not due to allergy, it occurs through a similar pathway.
Omalizumab has been designed to recognise and attach to a specific structure on circulating human IgE. This prevents IgE binding to high-affinity receptors (FcεRI) on the surface of mast cells and basophils, thus reducing receptor expression and the release of inflammatory mediators.
What are the risks associated with omalizumab use?
- A headache and injection site reactions (swelling, redness, pain, and itching) affect about 10% of patients treated with omalizumab.
- Omalizumab should not be used in people that may be hypersensitive (allergic) to the drug or any ingredient in the injection vial. It can rarely result in serious adverse reactions including anaphylaxis.
- See also: Immunisation in immunosuppressed dermatology patients for information on vaccination.
Omalizumab in inducible-urticaria
Chronic inducible urticaria, such as solar urticaria or cold urticaria, does not always respond well to antihistamines. To date, no randomised placebo-controlled trial of omalizumab has been performed in inducible urticarias but it has been reported to be effective in case reports.
IgE autoantibodies are also detected in a large number of patients with atopic dermatitis and bullous pemphigoid. In individual case reports, omalizumab treatment has been reported to be effective in some patients with these conditions. It has also been reported effective in chronic recurrent angioedema.
If you are not based in New Zealand, we suggest you refer to your national drug approval agency for further information about medicines (eg, the Australian Therapeutic Goods Administration and the US Food and Drug Administration) or a national or state-approved formulary (eg, the New Zealand Formulary and New Zealand Formulary for Children and the British National Formulary and British National Formulary for Children).