Balsalazide, a prodrug that is enzymatically cleaved by bacterial azoreduction to release equimolar quantities of mesalamine (5-aminosalicylic acid or 5-ASA) in the colon, an anti-inflammatory drug. The mechanism of action of 5-ASA is unknown, but appears to be local to the colonic mucosa rather than systemic. Balsalazide is indicated for the treatment of mildly to moderately active ulcerative colitis. Most frequently reported adverse events are: headache, abdominal pain, diarrhea, nausea, vomiting, respiratory infection, and arthralgia. The use of orally administered antibiotics could, theoretically, interfere with the release of mesalamine in the colon.