A 32-year-old man with newly diagnosed moderate ulcerative colitis (UC) presents with bloody diarrhea (6–8 stools/day), abdominal cramping, and mild systemic symptoms. Colonoscopy confirms continuous mucosal inflammation limited to the colon. Which is the drug of choice for induction of remission in this patient?

Explanation

## First-Line Induction Therapy in Moderate UC **Key Point:** Mesalamine (5-aminosalicylic acid) is the first-line agent for induction of remission in mild-to-moderate ulcerative colitis, particularly when disease is limited to the colon. ### Mechanism of Action Mesalamine acts as a topical anti-inflammatory agent in the colon by: - Inhibiting NF-κB and reducing pro-inflammatory cytokine production - Scavenging reactive oxygen species - Maintaining intestinal barrier function ### Dosing & Formulation - **Oral formulation:** 2.4–4.8 g/day in divided doses (pH-dependent or time-release coatings for colonic delivery) - **Rectal formulation:** Enemas or suppositories for left-sided/distal disease - **Onset:** 2–4 weeks for clinical response ### Evidence Base | Feature | Mesalamine | Corticosteroids | Biologics | |---------|-----------|-----------------|----------| | **First-line for mild–moderate UC** | Yes | No (second-line) | No (severe/refractory) | | **Maintenance of remission** | Yes, highly effective | No (not for maintenance) | Yes, but expensive | | **Systemic side effects** | Minimal | Significant (infection, hyperglycemia) | Immunosuppression, TB risk | | **Cost** | Low | Low | Very high | **High-Yield:** Mesalamine is effective for both **induction and maintenance** in UC; corticosteroids are used for induction in moderate–severe disease but NOT for maintenance due to lack of efficacy and side effects. **Clinical Pearl:** In this patient with moderate disease and no severe systemic symptoms (fever, tachycardia, severe anemia), mesalamine is preferred over corticosteroids to avoid unnecessary steroid exposure. ### When to Escalate - **Failure to respond in 2–4 weeks** → add corticosteroids or switch to biologic - **Severe disease (>6 stools/day, fever, elevated CRP)** → start corticosteroids concurrently with mesalamine - **Corticosteroid dependence or resistance** → infliximab or other TNF-α inhibitor [cite:Harrison 21e Ch 297]