A quantitative study of the effect of topical indomethacin on cutaneous erythema induced by UVB and UVC radiation.

The effect of indomethacin gel on UVB and UVC erythema was assessed objectively using a reflectance instrument. When indomethacin was applied immediately after irradiation, UVR (ultraviolet radiation) dose-dependent suppression of erythema was demonstrated for both wavelengths until 36 h after irradiation when both indomethacin and control gel base-treated sites were equally erythematous. Suppression of erythema also occurred when application of indomethacin was delayed until 24 h after irradiation, showing that for both wavelengths prostaglandin synthesis remains increased throughout this period. The degree of suppression at any time, however, was no greater than that achieved by a single application immediately after irradiation, indicating that the eventual equal erythema of indomethacin and gel base-treated sites was not due to tachyphylaxis or inadequate dosage. Construction of dose-response curves for the indomethacin-responsive and indomethacin-unresponsive components of erythema shows that in human skin the difference in erythemal response to UVB and UVC radiation is not due to the formation of different mediators at these wavelengths.