The role of antihistamines in the treatment of chronic urticaria. For many years, H1 antihistamines have been the primary management option for urticaria. However, undesirable side effects, particularly daytime sedation, have limited the usefulness of these classic antihistamines. A new class of peripherally acting, nonsedating antihistamines (e.g., terfenadine, astemizole, loratadine, and cetirizine) has proved to have clinical efficacy comparable with the classic antihistamines. In comparative trials between the various nonsedating agents, no significant difference in efficacy has been noted. All these agents have good safety profiles, although astemizole use has been correlated with increased appetite and weight gain in some patients, and cetirizine has caused slightly increased sedative effects compared with placebo. Although H1/H2 antihistamine combinations have been proposed as possible treatments for urticaria, studies have produced mixed results. 