What is the treatment for a patient with Irritable Bowel Syndrome (IBS) with constipation?

Treatment of IBS with Constipation (IBS-C)

Begin with soluble fiber (ispaghula/psyllium) 3-4 g/day, gradually increased to avoid bloating, combined with regular physical exercise as foundational therapy; if symptoms persist after 4-6 weeks, escalate to polyethylene glycol (PEG) as an osmotic laxative, and if still inadequate after 3 months, advance to linaclotide 290 mcg daily on an empty stomach as the preferred second-line agent. 1

First-Line Treatment: Lifestyle and Dietary Modifications

• Regular physical exercise should be recommended to all IBS-C patients as this improves global symptoms and forms the foundation of treatment 1

• Start with soluble fiber (ispaghula/psyllium) at 3-4 g/day, building up gradually to avoid bloating and gas, which is effective for both global symptoms and abdominal pain 1

• Avoid insoluble fiber (wheat bran) as it consistently worsens symptoms in IBS-C patients 1

• If soluble fiber fails after 4-6 weeks, consider a low FODMAP diet as second-line dietary therapy, but this must be supervised by a trained dietitian with planned reintroduction of foods according to tolerance 1

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

• Consider a 12-week trial of probiotics for global symptoms and abdominal pain, though no specific strain can be recommended; discontinue if no improvement occurs 1

Second-Line Treatment: Osmotic Laxatives

• Start polyethylene glycol (PEG) for constipation, titrating the dose according to symptoms, with abdominal pain being the most common side effect 1

• If PEG is insufficient after 2-4 weeks, add bisacodyl 10-15 mg once daily as a stimulant laxative, with a goal of one non-forced bowel movement every 1-2 days 1

• The dose of bisacodyl can be increased to 10-15 mg twice or three times daily if constipation persists 1

Third-Line Treatment: Prescription Secretagogues

• Linaclotide 290 mcg once daily on an empty stomach is the preferred second-line agent when first-line therapies fail, with strong recommendation and high-quality evidence 1, 2

• Linaclotide is the most effective FDA-approved secretagogue for IBS-C, addressing both abdominal pain and constipation 1, 2

• Linaclotide must be taken on an empty stomach at least 30 minutes before the first meal of the day to maximize efficacy 1

• Diarrhea is the most common adverse event with linaclotide, occurring as the mechanism of action 1

• If linaclotide is not tolerated or not covered by insurance, lubiprostone 8 mcg twice daily with food is an alternative FDA-approved secretagogue for women with IBS-C 1, 3

• Lubiprostone has a conditional recommendation with moderate certainty evidence, and nausea is the most common side effect (19% vs 14% with placebo) 1, 3

• Plecanatide is another alternative secretagogue with similar efficacy to linaclotide 1

Fourth-Line Treatment: Neuromodulators for Refractory Abdominal Pain

• Tricyclic antidepressants (TCAs) are effective for global symptoms and abdominal pain when other treatments fail 1

• Start amitriptyline at 10 mg once daily at bedtime, titrated slowly (by 10 mg/week) to 30-50 mg daily 1

• TCAs may worsen constipation through their anticholinergic effects, so use cautiously in IBS-C and ensure adequate laxative therapy is in place 1

• Continue TCAs for at least 6 months if symptomatic response occurs 1

• SSRIs may be effective as second-line neuromodulators for global symptoms when TCAs are not tolerated or worsen constipation 1

Fifth-Line Treatment: Psychological Therapies

• IBS-specific cognitive behavioral therapy (CBT) and gut-directed hypnotherapy should be considered when symptoms persist despite 12 months of pharmacological treatment 1

• These psychological therapies are effective for global symptoms with strong recommendation 1

Critical Pitfalls to Avoid

• Do not prescribe anticholinergic antispasmodics like dicyclomine or hyoscyamine in IBS-C, as they reduce intestinal motility and enhance water reabsorption, which will worsen the constipation 1

• Stop docusate (Colace) immediately as it lacks efficacy for constipation and evidence demonstrates no additional benefit 1

• Do not recommend IgG antibody-based food elimination diets as they lack evidence and may lead to unnecessary dietary restrictions 1

• Review efficacy after 3 months and discontinue ineffective therapies 1

• Do not continue ineffective therapies indefinitely; adjust the treatment plan based on response 1

Treatment Algorithm Summary

1. Start: Soluble fiber (3-4 g/day) + regular exercise 1
2. If inadequate after 4-6 weeks: Add PEG (osmotic laxative) 1
3. If inadequate after 2-4 weeks: Add bisacodyl (10-15 mg daily) 1
4. If inadequate after 3 months: Linaclotide 290 mcg daily (empty stomach) 1, 2
5. If refractory abdominal pain: Amitriptyline 10-50 mg nightly 1
6. If refractory after 12 months: CBT or gut-directed hypnotherapy 1