A sodium salt of a salicylate compound that is effectively bioconverted by colonic bacteria to mesalamine (5-aminosalicylic acid, 5-ASA), active component of olsalazine. Mechanism of action of mesalamine unknown. Thought to modulate local chemical mediators of inflammatory response, especially leukotrienes, and also postulated to be a free radical scavenger or inhibitor of tumor necrosis factor. Exerts local (not systemic) anti-inflammatory effects in GI tract. May reduce inflammation in colon by inhibiting cyclooxygenase and lipoxygenase, which catalyze formation of prostaglandin precursors (endoperoxides) and of leukotrienes and hydroxyeicosatetraenoic acids, respectively, from arachidonic acid and/or its metabolites.