Cetirizine. A reappraisal of its pharmacological properties and therapeutic use in selected allergic disorders.

Cetirizine, the carboxylated metabolite of hydroxyzine, is a specific and long-acting histamine H1-receptor antagonist. It has marked antiallergic properties and inhibits eosinophil chemotaxis during the allergic response. Clinical trial results indicate that cetirizine is an effective and well tolerated treatment for seasonal/perennial allergic rhinitis and chronic idiopathic urticaria in adults, and for seasonal/perennial allergic rhinitis in children. Cetirizine 10 mg/day appears to be as effective as conventional dosages of other established antihistamines such as astemizole, hydroxyzine, ketotifen, loratadine or terfenadine in relieving symptoms of these disorders, and is associated with a significantly lower incidence of sedation than hydroxyzine. However, when sedation was subjectively assessed, cetirizine appeared to be more sedating than placebo, loratadine or terfenadine in some clinical trials. This difference was not observed in several other double-blind studies. In contrast, when assessed objectively in pharmacodynamic comparisons, cetirizine was rarely more sedating than placebo or other second generation histamine H1-receptor antagonists. Cetirizine may also have a role in the treatment of certain forms of physical urticaria, atopic dermatitis and reactions to mosquito bites. In addition, it is being studied for the treatment of allergic asthma in adults and children. The pharmacokinetic profile and predominantly renal excretion of cetirizine suggest that this agent may have a reduced potential for adverse drug interactions involving hepatic enzyme systems compared with other histamine H1-receptor antagonists which are extensively metabolised. Thus, cetirizine, with its rapid onset and long duration of action, appears to provide a useful alternative to the antihistamine agents in clinical use.