Cimetidine's effect on dermal H1‐receptor antagonist tolerance.

The effect of the H2-receptor antagonist cimetidine upon H1-receptor antagonist tolerant histamine induced weal and flare responses was studied in nine healthy male subjects taking clemastine 1 mg orally twice a day. After 21 days clemastine therapy, the weal response became tolerant to clemastine but the flare response did not. Cimetidine, 400 mg, did not produce a significantly greater decrease in the area of the H1-receptor antagonist tolerant weal response than in the non-tolerant weal response. The results suggest that histamine mediated skin reactions may develop a tolerance to H1-receptor antagonist therapy that cannot be overcome by the addition of the H2-receptor antagonist cimetidine.