A 35-year-old woman with ulcerative colitis limited to the rectosigmoid region presents with mild-to-moderate disease activity. She has not received any prior treatment. What is the drug of choice for induction of remission?

Explanation

## First-Line Induction Therapy in Mild-to-Moderate Ulcerative Colitis **Key Point:** Mesalamine (5-aminosalicylic acid, 5-ASA) is the drug of choice for induction of remission in mild-to-moderate ulcerative colitis, regardless of disease extent. ### Why Mesalamine in UC? **High-Yield:** Unlike Crohn disease, aminosalicylates (5-ASA) are highly effective in ulcerative colitis for both induction and maintenance. They inhibit NF-κB and reduce prostaglandin synthesis in the colonic mucosa. **Clinical Pearl:** Mesalamine efficacy in UC is superior to in Crohn disease because UC is limited to the colon and rectum, where topical 5-ASA achieves high mucosal concentrations. Crohn disease involves the full thickness of bowel and can affect any segment from mouth to anus, making systemic therapy more necessary. ### Dosing and Formulation **Tip:** For mild-to-moderate UC: - **Oral mesalamine:** 2.4–4.8 g/day in divided doses - **Rectal mesalamine:** 1 g suppository or enema for distal disease (rectosigmoid) - **Combination therapy:** Oral + rectal for better response in distal disease ### Treatment Algorithm by Severity ```mermaid flowchart TD A[Ulcerative Colitis]:::outcome --> B{Disease Severity?}:::decision B -->|Mild-Moderate| C[Mesalamine 5-ASA]:::action B -->|Moderate-Severe| D[Corticosteroids ± 5-ASA]:::action B -->|Severe/Fulminant| E[IV Corticosteroids ± Anti-TNF]:::urgent C --> F[Assess response at 2-4 weeks]:::decision D --> F F -->|Remission| G[Maintain with 5-ASA]:::action F -->|No response| H[Escalate therapy]:::action ``` ### Comparative Efficacy: UC vs Crohn Disease | Feature | Ulcerative Colitis | Crohn Disease | |---------|-------------------|---------------| | **5-ASA efficacy** | High (induction & maintenance) | Low (minimal benefit) | | **First-line induction** | Mesalamine (mild-mod) | Corticosteroids | | **Corticosteroid role** | Reserved for moderate-severe | First-line for active disease | | **Maintenance** | 5-ASA monotherapy | Azathioprine, methotrexate | **Warning:** Do not confuse UC and Crohn disease treatment. Mesalamine is excellent in UC but poorly effective in Crohn disease; corticosteroids are essential in Crohn but reserved for moderate-severe UC. **Mnemonic:** **MUSE** — Mesalamine for UC, Steroids for Escalation. [cite:Harrison 21e Ch 297]