Augmentation of Ultraviolet Erythema by Indomethacin in Actinic Prurigo: Evidence of Mechanism of Photosensitivity

The effect of topical indomethacin on the intensity of erythema induced by ultraviolet radiation was measured by reflectance spectrophotometry in six patients with actinic prurigo. The intensity of UV‐C erythema was decreased by indomethacin in five patients. The intensity of UV‐B erythema was increased by indomethacin in five patients, and UV‐A erythema was increased by indomethacin in all patients. The increased inflammatory response induced by UV‐B and UV‐A with indomethacin application was related to erythemal sensitivity at these wavelengths. Topical indomethacin caused no change in the intensity of UV‐A erythema in a group of non‐photosensitive subjects. That inhibition of cyclo‐oxygenase augments the inflammatory response to ultraviolet radiation suggests that lipoxygenase metabolites of arachidonic acid may be involved in the mechanism of photosensitivity in actinic prurigo.