What medication and dietary measures should be recommended for an adult with diarrhea‑predominant irritable bowel syndrome who wants to reduce the frequency of bowel movements?

Treatment of Diarrhea-Predominant IBS

Loperamide 4–12 mg daily is the first-line medication to reduce stool frequency and urgency in diarrhea-predominant IBS. 1

First-Line Pharmacologic Management

Loperamide is the most effective initial treatment for reducing bowel frequency and urgency in IBS with diarrhea. 1

• Start with 2–4 mg taken up to four times daily, or use a single 4 mg dose at night 1
• Many patients learn to use loperamide prophylactically before situations where diarrhea would be problematic (e.g., before going out) 1
• Titrate the dose carefully to avoid constipation, bloating, and abdominal pain as side effects 1, 2
• Loperamide improves stool consistency and urgency but does not significantly improve abdominal pain 3, 4

Dietary Modifications to Implement Alongside Medication

• Reduce intake of poorly absorbed carbohydrates (lactose, fructose, sorbitol), caffeine, and alcohol 1, 3, 2
• For patients consuming substantial lactose (>280 mL milk/day), trial a lactose exclusion diet 1
• Avoid insoluble fiber (wheat bran) as it consistently worsens bloating and diarrhea symptoms 3
• Soluble fiber (psyllium/ispaghula) at 3–4 g/day may help improve stool consistency, but increase gradually to avoid gas and bloating 3

Second-Line Treatment for Persistent Abdominal Pain

If abdominal pain persists despite loperamide controlling diarrhea:

Tricyclic antidepressants are the most effective treatment for refractory abdominal pain in IBS-D. 1, 3

• Start amitriptyline 10 mg at bedtime 3
• Titrate by 10 mg weekly to a target of 30–50 mg daily 1, 3
• Continue for at least 6 months if symptomatic improvement occurs 3
• TCAs normalize rapid small bowel transit in diarrhea-predominant IBS through effects on gut motility and visceral nerve responses, independent of mood effects 1

Alternative for meal-related cramping:

• Dicyclomine (anticholinergic antispasmodic) taken before meals reduces meal-triggered abdominal pain 3
• Common side effects include dry mouth, visual disturbances, and dizziness 1, 3
• Peppermint oil provides antispasmodic effects with fewer side effects 1, 3

Third-Line Options for Refractory Cases

If loperamide and TCAs fail after 3 months:

• 5-HT3 antagonists (alosetron, ramosetron) reduce diarrhea but carry risk of ischemic colitis 4, 5, 6, 7
• Rifaximin (non-absorbable antibiotic) improves global symptoms but has limited effect on abdominal pain 3, 4, 5
• Eluxadoline (mixed opioid receptor modulator) addresses both diarrhea and pain 4, 5, 6

Special Consideration: Bile Acid Malabsorption

Approximately 10% of diarrhea-predominant IBS patients have bile acid malabsorption. 1

• Consider cholestyramine or colesevelam if diarrhea is severe or watery 1, 2
• Response to cholestyramine is best when SeHCAT retention is <5% 1
• However, tolerability is poor due to bloating and constipation; many patients prefer loperamide which is equally effective 1, 8

Psychological Therapies for Persistent Symptoms

When symptoms persist despite 12 months of pharmacologic treatment:

• IBS-specific cognitive-behavioral therapy improves global symptom burden 3
• Gut-directed hypnotherapy is effective for overall symptom improvement 3

Critical Pitfalls to Avoid

• Do not use codeine (15–30 mg, 1–3 times daily) as first-line despite its effectiveness in functional diarrhea, because it causes sedation and drug dependency 1
• Do not prescribe fiber supplements containing wheat bran as they worsen bloating and pain 3
• Review efficacy after 3 months and discontinue ineffective therapies 3
• Do not recommend IgG antibody-based food elimination diets as they lack evidence and lead to unnecessary restrictions 3