A patient with Crohn's disease affecting the terminal ileum is started on sulfasalazine. Which component is responsible for the therapeutic effect in IBD?
- A 5-aminosalicylic acid (mesalazine), which has topical anti-inflammatory action on the colonic mucosa ✓
- B Sulfapyridine, which suppresses lymphocyte proliferation
- C The intact sulfasalazine molecule, which inhibits TNF-alpha systemically
- D Sulfapyridine, which inhibits leukotriene synthesis in intestinal mucosa
Correct answer: A. 5-aminosalicylic acid (mesalazine), which has topical anti-inflammatory action on the colonic mucosa
Explanation
Sulfasalazine is a prodrug consisting of 5-aminosalicylic acid (5-ASA/mesalazine) linked by an azo bond to sulfapyridine. Colonic bacteria cleave this bond, releasing 5-ASA locally in the colon; 5-ASA inhibits prostaglandin and leukotriene synthesis and scavenges free radicals in the colonic mucosa. Sulfapyridine is the carrier that prevents small intestinal absorption of 5-ASA; sulfapyridine itself is responsible for most systemic adverse effects (haemolytic anaemia, agranulocytosis, hepatotoxicity).
Reference: KD Tripathi, Essentials of Medical Pharmacology, 8th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.