A 28-year-old woman with ulcerative colitis confined to the rectum and sigmoid colon presents with 6–8 bloody stools daily, tenesmus, and mild systemic symptoms. Flexible sigmoidoscopy shows continuous mucosal erythema, friability, and ulceration limited to the rectosigmoid. Laboratory studies are unremarkable except for mild anemia (Hb 10.2 g/dL). What is the drug of choice for induction of remission in this patient?

Explanation

## First-Line Therapy in Mild-to-Moderate Ulcerative Colitis **Key Point:** 5-aminosalicylic acid (5-ASA) agents—mesalamine, sulfasalazine, or olsalazine—are the gold-standard first-line induction therapy for mild-to-moderate ulcerative colitis, particularly when disease is limited to the rectosigmoid. ### Why Mesalamine Is Preferred 1. **Disease severity:** Mild-to-moderate UC (6–8 stools/day, mild anemia, normal inflammatory markers) is appropriate for 5-ASA monotherapy. 2. **Mechanism:** 5-ASA acts topically on the colonic mucosa, reducing mucosal inflammation and prostaglandin-mediated cytokine release. 3. **Efficacy:** Induces remission in 50–70% of patients with mild-to-moderate disease within 4–6 weeks. 4. **Safety:** Well-tolerated with minimal systemic side effects; preferred over sulfasalazine due to better tolerability (fewer GI and hematologic adverse effects). 5. **Disease distribution:** Rectosigmoid disease responds particularly well to topical 5-ASA (suppositories or enemas) combined with oral mesalamine. ### Comparative Efficacy in UC | Severity | First-Line | Second-Line | Biologic | |----------|-----------|------------|----------| | **Mild-to-moderate** | 5-ASA (mesalamine) | Corticosteroids | — | | **Moderate-to-severe** | 5-ASA + corticosteroids | Azathioprine | TNF-α inhibitor | | **Severe/fulminant** | IV corticosteroids | Cyclosporine | Infliximab | **Clinical Pearl:** UC is a mucosal disease (unlike Crohn disease, which is transmural); therefore, topical and oral 5-ASA agents are highly effective. The continuous distribution of inflammation and lack of skip lesions further support 5-ASA as first-line. **High-Yield:** Mesalamine is preferred over sulfasalazine because sulfasalazine carries higher rates of nausea, headache, and reversible oligospermia. Both are equally effective, but mesalamine is better tolerated. **Mnemonic:** **ASACOL** = 5-ASA Colon = topical action on colon (mesalamine brand name; indicates its site of action).