Inhibition of histamine and allergen skin wheal by cetirizine in four animal species.

Histamine-induced skin reactions were studied in four animal species. Cetirizine displayed very potent oral antihistaminic activity in this model. In rats, the dose that reduced the reaction by 50% in comparison to controls was 4.2 mumol/kg and between 0.1 and 0.4 mumol/kg for the other species (mice, guinea pigs, and dogs). Cetirizine also inhibited the immediate hypersensitivity reaction induced by Ascaris extract in dogs. By the oral route, cetirizine had a more potent and longer acting activity than mepyramine, clemastine, terfenadine, astemizole, and hydroxyzine.