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Author: Anoma Ranaweera B.V. Sc; PhD (Clinical Biochemistry, University of Liverpool, UK), 2013.
Omalizumab is a humanised monoclonal antibody that binds to circulating immunoglobulin E (IgE) and reduces the release of inflammatory mediators from mast cells and basophils.
It is currently licensed as add-on therapy for patients with severe, persistent allergic asthma. It is given by subcutaneous injection once every 4 weeks.
Omalizumab has also been reported to be highly effective in treating severe chronic spontaneous urticaria in teenagers and adults.
The trade name of omalizumab is Xolair™.
Chronic spontaneous urticaria (also called chronic idiopathic urticaria) is defined as hives or wheals 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 wheal. Histamine also affects sensory nerves, resulting in neurogenic flare (red skin) and pruritus (itch).
Chronic urticaria may be refractory to antihistamines and associated with a pronounced cellular infiltrate.
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.
Omalizumab is currently in phase III clinical trials in chronic spontaneous urticaria.
The immunoglobulin "E" (IgE) triggers an allergic reaction (e.g. asthma) in response to an allergen (e.g. 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.
Results of at least 2 published randomised controlled trials support the efficacy of omalizumab in chronic spontaneous urticaria.
|Omalizumab 300 mg||-9.8||< 0.001|
|Omalizumab 150 mg||-8.1||= 0.001|
|Omalizumab 75 mg||-5.9||= 0.46|
So far, there is no evidence that omalizumab is disease modifying. When patients stopped the study drug, their symptoms recurred. At the end of 16 weeks off treatment, symptoms of urticaria were similar to patients treated with placebo.
Inducible or physical 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.
IgE autoantibodies are also detected in a large number of patients with atopic dermatitis and bullous pemphigoid. In 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. Randomised controlled trials are warranted.
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