Suppression of histamine-induced pruritus by three antihistaminic drugs.

A double-blind crossover study of inhibition of histamine-induced pruritus by three commonly prescribed antihistamines was conducted on 28 normal subjects. Drugs used included diphenhydramine HCl (Benadryl), cyproheptadine (Periactin), hydroxyzine HCl (Atarax), and a lactose placebo in identical capsules. Intradermal histamine dose-response thresholds of pruritus were obtained before and after pretreatment with the three antihistamines and placebo in each subject. Analysis of data revealed a fivefold increase above baseline of the histamine dose required to produce pruritus following both cyproheptadine and placebo. This compared to a tenfold increase following diphenhydramine and a 750-fold increase following hydroxyzine HCl. The most common side effect was drowsiness, which occurred with all three drugs.