[Antipruritic effect of antihistaminic and local anesthetic topical agents after iontophoretic histamine stimulation].

No adequate topical therapy is available for pruritus. As little is known about the local influence of antihistamines and topical anaesthetics on the pruritic effect of histamine, we studied these agents in 12 volunteers. The antipruritic effect of 15-min topical application of dimethindene maleate (Fenistil gel) and different agents (Optiderm, EMLA, Xylocaine-Salbe 5%) on subsequent focal histamine stimulus (20 mC) given by iontophoresis was evaluated. The results were compared with those of pretreatment with the corresponding placebo creams and observations on skin. Wheal and flare areas were evaluated planimetrically. Itch or pain ratings were entered on a scale every minute over a 24-min period. The examination also comprised alloknesis, i.e. elicitation of perifocal itch sensation by usually non-itch-inducing (e.g. mechanical) stimuli. Remarkably, all topically applied substances, regardless of antihistaminic or anaesthetic potential, reduced the area of alloknesis significantly. This is likely to be a result of diminished excitability of the cutaneous mechanoreceptors. Itching was significantly reduced by all active substances, including the placebo cream corresponding to Optiderm, which might be due to the presence of urea.