The monoclonal IgE antibody omalizumab is getting a lot of attention these days, and so it should. FDA-approved for use in patients with allergic asthma, it has also been used experimentally to treat allergic rhinitis, chronic urticaria, food allergies and idiopathic anaphylaxis. The last-named use is particularly intriguing, because it is clear that omalizumab can prevent anaphylaxis in some patients, but it can also cause a life-threatening anaphylactic reaction in others.
When Xolair was first approved for use in the US in 2003, The Medical Letter was tempered in its enthusiasm:
“Omalizumab (Xolair) is an anti-IgE antibody that can reduce the number of asthma exacerbations and decrease use of inhaled corticosteroids in patients with allergic asthma, but the clinical effects are not as impressive as the remarkable reduction in circulating free IgE. The high cost of this treatment, the need for subcutaneous injections, and concerns about its long-term safety will probably restrict its use to patients with severe asthma, not adequately controlled by other drugs, that has a clear allergic component. For other patients with asthma, spending $10,000-$12,000 a year and running the risk, however remote, of anaphylaxis or developing a malignancy for such a small improvement can hardly be justified. Highly food-allergic patients, such as those who run the risk of dying from inadvertent exposure to peanuts, might be a better target population for a drug like this one.”
Now, 10 years later, that still sounds reasonable. Anaphylactic reactions to the drug have occurred, at a rate of 0.2% of patients treated, according to the FDA. A Medical Letter In Brief in 2007 brought the disconcerting news that some of these reactions occurred up to 4 days after an injection, which makes them difficult to monitor. Nevertheless, interest has grown in use of the drug for indications other than asthma. We will be reassessing it soon in The Medical Letter for treatment of chronic urticaria and in Treatment Guidelines from The Medical Letter for treatment of allergic rhinitis and other allergic disorders. Omalizumab has also been used, as we anticipated 10 years ago, in patients with serious food allergies, with some good results. One worth sharing was a well-documented case report of a 16-year-old girl who had had multiple allergic reactions, including laryngeal angioedema, when she was exposed to the vapors of roasting poultry; after 2 injections of omalizumab, she was cured. How about that?