Mechanism of chronic urticaria exacerbation by aspirin.

In some patients with chronic idiopathic urticaria (CIU), aspirin and other nonsteroidal anti-inflammatory drugs (NSAIDs) that inhibit cyclooxygenase 1 (COX-1) precipitate wheals and swelling. There is no in vitro diagnostic, and diagnosis can be established only by provocation challenges with aspirin or other NSAIDs. Skin reactions triggered by aspirin are associated with the inhibition of cyclooxygenase, specifically COX-1, but not COX-2, and are characterized by overproduction of cysteinyl leukotrienes (cys-LTs). Aspirin and other NSAIDs should be avoided, but highly specific COX-2 inhibitors, known as coxibs, are well tolerated and can probably be safely used. Evidence has been accumulated that these reactions are due to the interference of aspirin-like drugs with arachidonic-acid metabolism. In this article, we discuss the mechanism of these reactions, and the characteristic course of aspirin-induced urticaria and its management.