A comparison of astemizole and chlorpheniramine in dermographic urticaria.

The effects of the H I receptor antagonists astemizole and chlorpheniramine on dermographism were compared in a double-blind study in sixteen patients. Both drugs resulted in a parallel and significant depression of the dermographic force-response curve and an elevation of the weal-force threshold, but the changes were greater in the patients receiving astemizole (a maximal potency shift of 74% for astemizole and 37% for chlorpheniramine). Subjective itch (10 cm line) and frequency of dermographic episodes were also reduced more by astemizole than by chlorpheniramine. The effect of astemizole was greater at 4 weeks than at 2 weeks, whereas the effect of chlorpheniramine had decreased at 4 weeks. The effect of astemizole but not chlorpheniramine was still apparent 4 weeks after treatment had been stopped. Since the degree of residual dermographism was comparable despite great differences in histamine weal inhibition a vasoactive mechanism in addition to that mediated by histamine must be involved in dermographic urticaria.