Suppression of histamine-induced pruritus by hydroxyzine and various neuroleptics.

This study evaluates the ability of hydroxyzine and various neuroleptics to suppress histamine-induced pruritus in ten volunteer subjects with the use of a double-blind crossover protocol. The itch threshold was determined in each volunteer by intradermal injection of gradually increasing concentrations of histamine. Volunteers were then given the study drugs and placebo at the same interval of time, under near identical conditions, and the itch threshold was determined. Thiothixene, hydroxyzine hydrochloride, chlorpromazine, thioridazine, and a lactose placebo were evaluated. Compared to other drugs, hydroxyzine alone was more effective in the suppression of histamine-induced itch. Consequently, hydrozyzine may be more effective in histamine-induced pruritus. The neuroleptic drugs used in this study do not significantly suppress histamine-induced pruritus, but they may be beneficial in nonhistamine-induced pruritus or psychogenic pruritus.