CETIRIZINE - A REAPPRAISAL OF ITS PHARMACOLOGICAL PROPERTIES AND THERAPEUTIC USE IN SELECTED ALLERGIC DISORDERS

Cetirizine, the carboxylated metabolite of hydroxzine, is a specific a nd long-acting histamine H-1-receptor antagonist. It has marked antial lergic properties and inhibits eosinophil chemotaxis during the allerg ic response. Clinical trial results indicate that cetirizine is an eff ective and well tolerated treatment for seasonal/perennial allergic rh initis and chronic idiopathic urticaria in adults, and for seasonal/pe rennial allergic rhinitis in children. Cetirizine 10 mg/day appears to be as effective as conventional dosages of other established antihist amines such as astemizole, hydroxyzine, ketotifen, loratadine or terfe nadine in relieving symptoms of these disorders, and is associated wit h a significantly lower incidence of sedation than hydroxyzine. Howeve r when sedation was subjectively assessed, cetirizine appeared to be m ore 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 co mparisons, cetirizine was rarely more sedating than placebo or other s econd generation histamine H-1-receptor antagonists. Cetirizine may al so have a role in the treatment of certain forms of physical urticaria , atopic dermatitis and reactions to mosquito bites. In addition, it i s being studied for the treatment of allergic asthma in adults and chi ldren. The pharmacokinetic profile and predominantly renal excretion o f cetirizine suggest that this agent may have a reduced potential for adverse drug interactions involving hepatic enzyme systems compared wi th other histamine H-1-receptor antagonists which are extensively meta bolised. Thus, cetirizine, with its rapid onset and long duration of a ction, appears to provide a useful alternative to the antihistamine ag ents in clinical use.