Which medication in the listed regimens functions as an immunosuppressant for ulcerative colitis?

• A. Diphenoxylate
• B. Prednisone
• C. Sulfasalazine
• D. Azathioprine

Answer: (D)

Immunosuppressants in ulcerative colitis are used to dampen the overactive immune response that drives ongoing inflammation, helping to maintain remission and reduce the need for steroids. Azathioprine fits this role because it is a purine analog that inhibits DNA synthesis in rapidly dividing immune cells, particularly T and B lymphocytes. By limiting these cells’ proliferation, it lowers the immune system’s attack on the colon and supports longer-term disease control, often as a steroid-sparing agent.

Prednisone, a corticosteroid, also reduces inflammation quickly, but it’s typically used for short-term induction rather than long-term maintenance due to significant side effects with prolonged use. Diphenoxylate acts as an anti-diarrheal and doesn’t address immune activity. Sulfasalazine is a 5-aminosalicylic acid compound with anti-inflammatory effects in the gut and some immunomodulatory actions, but it’s not a classic systemic immunosuppressant like azathioprine.

So, azathioprine is the medication that functions as an immunosuppressant in UC, especially for maintaining remission and reducing steroid requirements.