Topical indomethacin aggravates the weal and flare response in chronic dermographic urticaria: evidence for a new class of histamine receptors.

The effect of topical indomethacin on the weal and flare response was measured in 9 patients with chronic dermographic urticaria. An augmentation of dermographic wealing by topical indomethacin was shown with lowering of the weal threshold from 22.3 +/- 4.7 g/mm2 (mean +/- SEM, n = 9) to 16.4 +/- 3.8 (p < 0.005), but without a change in the shape of the force/response curve. Flare was increased by indomethacin particularly in patients with a greater lowering of the weal threshold. The augmentation of weal and flare by indomethacin in individual patients was not related to the degree of inhibition of UVB erythema in individual patients. These findings indicate that in chronic dermographic urticaria there is an abnormality involving eicosanoid production by a non-cyclo-oxygenase pathway. It is suggested that this acts by augmenting the effect of histamine on a new class of histamine receptor, the definition and antagonism of which should lead to better control of urticarial disease.