Histamine, antihistamines and atopic eczema.

Histamine is known to be a classical inducer of pruritus. In atopic eczema, itch is a prominent feature (regarded by some even as a 'primary lesion'!). One of the most potent chemical mediators of itch is histamine. Histamine, together with other mediators may play a role in the pathophysiology of atopic eczema: the increased release of histamine from basophil leucocytes of atopic patients has been described, as well as elevated histamine levels in plasma and skin during acute exacerbations of eczematous lesions. Therefore, application of H1 antagonists seems to be a rational regime in the symptomatic treatment of atopic eczema. Nevertheless, some controversy exists regarding the clinical efficacy of orally applied H1 antagonists in this disease, especially with regard to the newer non-sedating compounds such as terfenadine, astemizole, loratadine and cetirizine. Review of the literature shows that there are studies demonstrating a clear-cut antipruritic effect of non-sedating H1 antagonists. Thus the sedative action does not seem necessarily to be connected with therapeutic efficacy in treating itch in atopic eczema. Newer studies show that cetirizine exerts an additional inhibitory effect on eosinophils. This may broaden the therapeutic spectrum of this H1 antagonist in diseases with eosinophil involvement.