What are the treatment options for a patient with Irritable Bowel Syndrome with Constipation (IBS-C)?

Treatment of IBS-C

Start with soluble fiber (psyllium/ispaghula) at 3-4 g/day, gradually titrating upward, and if symptoms persist after 4-6 weeks, escalate to linaclotide 290 mcg daily on an empty stomach as the preferred second-line agent. 1

First-Line Treatment: Lifestyle and Dietary Interventions

Soluble fiber is the cornerstone of initial therapy:

• Begin with psyllium or ispaghula at 3-4 g/day and build up gradually to avoid bloating and gas 1
• Optimal dosing is >10 g/day with treatment duration of at least 4 weeks for improving stool frequency and consistency 1
• Avoid insoluble fiber (wheat bran, whole grains) entirely—it consistently worsens bloating and abdominal pain in IBS-C 1

Regular physical exercise should be recommended to all IBS-C patients as foundational therapy 1

Common Pitfall to Avoid:

Do not recommend gluten-free diets unless celiac disease has been confirmed—evidence does not support their use in IBS-C 1

Second-Line Treatment: Prescription Secretagogues

When first-line therapies fail after 4-6 weeks, linaclotide is the most effective and preferred agent:

• Linaclotide 290 mcg once daily on an empty stomach (at least 30 minutes before first meal) is the gold standard second-line treatment 1, 2
• This guanylate cyclase-C agonist improves both constipation and abdominal pain 1, 2
• Diarrhea is the most common side effect but is generally manageable and occurs as the mechanism of action 1

Alternative secretagogues if linaclotide is not tolerated:

• Lubiprostone 8 mcg twice daily with food is an alternative, though it has higher rates of nausea (19% vs 14% placebo) 1, 3
• Lubiprostone is FDA-approved specifically for IBS-C in women ≥18 years old 3
• Take with food and water to reduce nausea 3

Review efficacy after 3 months and discontinue if no response 1

Third-Line Treatment: Neuromodulators for Refractory Abdominal Pain

For persistent abdominal pain despite adequate laxative therapy:

• Tricyclic antidepressants (TCAs) are the most effective option, starting with amitriptyline 10 mg once daily at bedtime 1
• Titrate slowly (by 10 mg/week) to 30-50 mg daily 1
• Critical caveat: TCAs may worsen constipation through anticholinergic effects—ensure adequate laxative therapy is in place before initiating 1
• Continue for at least 6 months if symptomatic response occurs 1

SSRIs may be effective as alternative neuromodulators when TCAs worsen constipation or are not tolerated 1

Fourth-Line Treatment: Psychological Therapies

For symptoms persisting despite 12 months of pharmacological treatment:

• IBS-specific cognitive behavioral therapy (CBT) or gut-directed hypnotherapy should be recommended 1
• These therapies have demonstrated efficacy for abdominal pain and global symptoms 1

Critical Errors to Avoid

Do NOT prescribe anticholinergic antispasmodics (dicyclomine, hyoscyamine) for IBS-C:

• These agents reduce intestinal motility and enhance water reabsorption, which will worsen the constipation 1
• This is a common error when prescribing based solely on "IBS" diagnosis without considering the constipation subtype 1

Do NOT recommend:

• IgG antibody-based food elimination diets—they lack evidence and may lead to unnecessary dietary restrictions 1
• Extensive testing once IBS-C diagnosis is established 1

Treatment Algorithm Summary

1. Weeks 0-6: Soluble fiber (psyllium) 3-4 g/day gradually increased + regular exercise 1
2. If inadequate response at 6 weeks: Add linaclotide 290 mcg daily on empty stomach 1, 2
3. If persistent pain at 3 months: Add amitriptyline 10 mg nightly (with adequate laxative coverage) 1
4. If symptoms persist at 12 months: Refer for IBS-specific CBT or gut-directed hypnotherapy 1

Review treatment efficacy every 3 months and discontinue ineffective medications 1