N-acetyl-5-Aminosalicylic acid is a metabolite of the anti-inflammatory agent 5-aminosalicylic acid and its prodrug form, sulfasalazine . It is formed in the liver, intestinal lumen, and colonic epithelial cells via N-acetyltransferases. It reduces IFN-γ binding to colonic epithelial cells by 24% when used at a concentration of 10 mM. N-acetyl-5-Aminosalicylic acid (100 µM) scavenges 2,2-diphenyl-1-picrylhydrazyl radicals in a cell-free assay and inhibits base hydroxylation in DNA stimulated by hydroxy radicals. Unlike sulfasalazine, N-acetyl-5-aminosalicylic acid does not inhibit 15-hydroxy prostaglandin dehydrogenase (PGDH). Urinary levels of N-acetyl-5-aminosalicylic acid have been used as a marker of 5-ASA adherence in patients with inflammatory bowel disease.