Summary The effect of a potent antihistamine, cetirizine, was studied on allergic patients and normal subjects by means of an in‐vivo‘skin window’ technique. All subjects showed significant inhibition of skin‐test responses to grass pollen, compound 48/80, histamine and methacholine, after administration of a single dose (10 mg) of cetirizine. Compared to placebo, cetirizine significantly decreased the eosinophils attraction at skin sites challenged with grass pollen and compound 48/80. In allergic patients no change in eosinophil migration pattern was noted with histamine and methacholine skin‐tested sites. In normal subjects, compound 48/80 and histamine did not induce eosinophil accumulation and cetirizine did not modify cellular patterns as compared to placebo. These results suggest that cetirizine acts on eosinophil migration by inhibiting the release of mast cell mediators or inhibiting the eosinophilotactic mediators themselves.

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These results suggest that cetirizine reduced the release of IL-8 from A549 cells stimulated with PMA and TNF-alpha, respectively, by lowering IL-8 gene expression. Therefore, cetirizine might exert anti-inflammatory effects beyond its H1-receptor antagonistic activity in the course of inflammatory respiratory tract disorders such as bronchial asthma and allergic rhinitis.

Neither cetirizine nor loratadine inhibited codeine-induced histamine release or modified the time course of its release in human skin in vivo when given in clinically used doses which are sufficient to significantly reduce weal and flare responses.