Efficacy measurement of topical antihistamines: a review.
More and more antihistamines are used in gels or ointments for local antipruritic therapy. Among other factors, the efficacy is dependent on the penetration properties of the respective agents and the optimal choice of vehicle substances. To avoid expensive treatment with unsatisfying success, a reliable efficacy measurement would be desirable prior to the admission of new topical antihistamine preparations. Therefore we reviewed the literature for common methods to assess the efficacy of local antihistamines in healthy volunteers. The principle is to apply the test substance to marked test areas and to challenge the skin after a certain time with a standardised amount of histamine, allergens or mast-cell-degranulating substances. For the test evaluation, the areas of wheal, flare and itch are measured and compared between antihistamine-treated and control fields. Challenge models and most of the described evaluation methods are suited for the preliminary efficacy measurement of antihistamines. However, to be able to compare the results, a standardised procedure used by all investigators would be desirable.