Separate effects of topical indomethacin on the itch response and on the flare reaction induced by histamine in human skin.

The effects of topical indomethacin on histamine responses and histamine release were studied in 15 healthy volunteers. Three hours before testing, the indomethacin solution was applied under occlusion on one arm and the corresponding vehicle on the other. Solutions of histamine and the histamine releasing compound 48/80 were injected intradermally in both arms. Indomethacin treatment inhibited the flare reactions induced by histamine and compound 48/80 to about 50%, whereas no influence was seen on the itch responses. Our results indicate that indomethacin has no effect on the release of histamine, but it selectively suppresses the histamine-induced flare reaction leaving the itch duration unaffected.