What medication regimen is recommended for an adult with constipation‑dominant irritable bowel syndrome presenting with intermittent epigastric pain, bloating, flatulence and frequent scant stools, without fever, vomiting, weight loss, or gastrointestinal bleeding?

Medications for Constipation-Predominant IBS

For an adult with constipation-dominant IBS presenting with intermittent epigastric pain, bloating, flatulence and infrequent scant stools, start with soluble fiber (psyllium/ispaghula) 3-4 g daily, add an osmotic laxative (polyethylene glycol) if fiber fails after 4-6 weeks, then escalate to linaclotide 290 mcg daily on an empty stomach if symptoms persist after 3 months of laxative therapy. 1, 2

First-Line Treatment: Soluble Fiber and Lifestyle

• Begin with soluble fiber (psyllium or ispaghula) at 3-4 g/day, gradually increasing the dose to minimize bloating and gas, which is effective for both global IBS-C symptoms and abdominal pain. 1, 2

• Explicitly avoid insoluble fiber (wheat bran) as it consistently worsens bloating, pain, and overall symptom burden in IBS-C patients. 1, 2

• Recommend regular physical exercise to all IBS-C patients as foundational therapy, as this improves global symptoms independent of pharmacologic treatment. 1, 2

• Provide basic dietary counseling: limit excess caffeine, ensure adequate time for regular defecation, and correct any inappropriate self-imposed dietary restrictions that may worsen constipation. 2

Second-Line Treatment: Osmotic Laxatives

• If soluble fiber fails after 4-6 weeks, add polyethylene glycol (PEG) as an osmotic laxative, titrating the dose according to symptom response; abdominal pain is the most common side effect. 1, 2

• Review efficacy after 3 months and discontinue if no meaningful improvement occurs, as continuing ineffective therapies indefinitely provides no benefit and may reinforce illness behavior. 1, 2

Third-Line Treatment: Prescription Secretagogues

• Linaclotide 290 mcg once daily on an empty stomach (at least 30 minutes before the first meal) is the preferred prescription agent for IBS-C when first-line therapies fail, with high-quality evidence supporting its efficacy for both abdominal pain and constipation. 1, 2

• Linaclotide is the most effective FDA-approved secretagogue for IBS-C, demonstrating superiority over placebo in meeting FDA response endpoints at 12-week follow-up in multiple large randomized controlled trials involving over 6,000 patients. 1

• Plecanatide 3 mg daily is an alternative secretagogue with similar efficacy to linaclotide if the latter is not tolerated or not covered by insurance. 1

• Lubiprostone 8 mcg twice daily with food is a third-line option for women with IBS-C, though it carries a conditional recommendation due to moderate-certainty evidence and higher rates of nausea (19% vs 14% with placebo). 1, 2

• Diarrhea is the most common adverse event with linaclotide, occurring as the mechanism of action; review efficacy after 3 months and discontinue if no response. 2, 3

Managing Abdominal Pain in IBS-C

• For meal-related abdominal pain, consider peppermint oil as an antispasmodic with a favorable side-effect profile before escalating to other agents. 1, 2, 4

• Avoid anticholinergic antispasmodics (dicyclomine, hyoscyamine) in IBS-C patients, as their mechanism of reducing intestinal motility and enhancing water reabsorption will worsen the constipation. 1, 2, 4

• For persistent abdominal pain despite adequate treatment of constipation, tricyclic antidepressants (amitriptyline) are the most effective option, starting at 10 mg nightly and titrating slowly (by 10 mg/week) to 30-50 mg daily. 1, 2

• Use tricyclic antidepressants cautiously in IBS-C and ensure adequate laxative therapy is in place, as their anticholinergic effects can worsen constipation; continue for at least 6 months if symptomatic response occurs. 1, 2

• Selective serotonin reuptake inhibitors (SSRIs) may be considered as an alternative when tricyclic antidepressants are not tolerated or worsen constipation, though evidence for their efficacy is weaker than for tricyclics. 1, 2

Fourth-Line Treatment: Psychological Therapies

• IBS-specific cognitive-behavioral therapy (CBT) and gut-directed hypnotherapy should be considered when symptoms persist despite 12 months of optimal pharmacological treatment, as both have demonstrated effectiveness in reducing overall symptom burden. 1, 2

• Psychological interventions are adjuncts rather than replacements for pharmacotherapy, as they do not improve constipation or persistent abdominal pain when used alone. 2

Critical Pitfalls to Avoid

• Do not prescribe anticholinergic antispasmodics (dicyclomine, hyoscyamine) for IBS-C, as they reduce intestinal motility and enhance water reabsorption, which will worsen the constipation. 1, 2, 4

• Do not continue docusate (Colace) as it lacks efficacy for constipation; evidence demonstrates that adding docusate to senna provides no additional benefit compared to senna alone. 2

• Do not recommend IgG antibody-based food elimination diets or gluten-free diets unless celiac disease has been confirmed, as evidence does not support their use in IBS-C and they may lead to unnecessary dietary restrictions. 1, 2

• Do not use opioid analgesics for IBS-related pain, as they cause opioid-induced bowel dysfunction and worsen constipation. 2

• Explain to patients that complete symptom resolution is often not achievable; the goal is symptom relief and improved quality of life, not cure. 2

Treatment Algorithm Summary

1. Start soluble fiber (psyllium 3-4 g/day) + lifestyle modifications (exercise, dietary counseling) 1, 2
2. Add polyethylene glycol if fiber fails after 4-6 weeks 1, 2
3. Escalate to linaclotide 290 mcg daily if symptoms persist after 3 months of laxative therapy 1, 2
4. For persistent pain despite adequate constipation treatment, add amitriptyline 10-50 mg nightly 1, 2
5. Consider IBS-specific CBT or gut-directed hypnotherapy if refractory after 12 months 1, 2