Omalizumab (Xolair®) is a recombinant humanized monoclonal antibody that binds specifically to the FcEpsilonR1 binding site on human IgE. The binding of omalizumab inhibits the ability of IgE to bind to basophils or mast cells. Free IgE levels fall by 89% and 98% over 16 and 24 weeks of therapy respectively (Busse, 2001). Total IgE levels rise in patients treated with omalizumab though almost all IgE is bound and thus inactive. Omalizumab has also been shown to decrease expression of the FcEpsilonR1 receptor on both basophils and mast cells (Beck et al, 2004). Omalizumab recently received FDA approval for the treatment of moderate to severe persistent allergic asthma in pediatric (12 years of age and above) and adult patients. Studies have also shown efficacy in the treatment of allergic rhinitis and similar anti-IgE compounds have been efficacious as food allergy therapeutics (Casale, 2001, and Leung 2003).

Given the efficacy of omalizumab in the treatment of moderate to severe allergic asthma, the researchers will conduct a double-blind study to evaluate the safety and efficacy of omalizumab in a small number of patients with chronic urticaria with persistent symptoms in spite of background antihistamine therapy. Omalizumab is currently not indicated for patients with chronic urticaria. The primary hypothesis is that omalizumab will lead to a reduction in serum IgE levels and blood basophil high affinity IgE receptor expression in subjects with chronic idiopathic urticaria. Additionally, clinical outcomes such as quality of life, symptoms scores, and medication use will be explored. This study should allow for further understanding of the role IgE plays in chronic urticaria.