Etodolac is the first anti-inflammatory drug belonging to the tetrahydropyranoindole class. In contrast to several other common anti-inflammatory drugs, etodolac exhibited an unusually high potency as an inhibitor of established adjuvant arthritis relative to its activity against carrageenan paw edema in the rat. This phenomenon led us to investigate whether the ability of NSAIDs to inhibit prostaglandin biosynthesis differed between cultures of macrophages, which are present in inflammatory exudates, and cultures of synoviocytes and chondrocytes, which contribute to inflammation of the articulating joint. Although other anti-inflammatory drugs were found to be equally active in all three cell types, etodolac was found to be much more effective on the cells of the joint than on the macrophage. This differential activity may be responsible for the striking efficacy of etodolac as an anti-arthritic drug.

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