ZYRTEC®, a metabolite of hydroxyzine, is an anti-allergic agent with a histamine H1 receptor antagonism devoid of any significant anticholinergic and antiserotonin effects as demonstrated in experimental and clinical pharmacology.
At the present stage of research into the mode of action of cetirizine, the anti-allergic activity seems to be exerted mainly via its effects on the release of certain mediators, such as histamine, together with a selective action on the H1 receptors. Cetirizine reduces eosinophil recruitment induced by an antigen-antibody reaction.