What is the appropriate treatment approach for an adult with irritable bowel syndrome with predominant constipation (IBS‑C) and no alarm features?

Treatment of Irritable Bowel Syndrome with Constipation (IBS-C)

Start with soluble fiber (ispaghula/psyllium) at 3–4 g daily, titrate upward gradually, and add regular aerobic exercise as the foundation of IBS-C therapy. 1, 2

First-Line Therapy: Lifestyle and Dietary Interventions

• Recommend regular aerobic exercise to all IBS-C patients as this independently improves global symptom scores and should be instituted before pharmacologic therapy. 1, 2

• Initiate soluble fiber (ispaghula/psyllium) at 3–4 g per day and build up gradually to minimize bloating and gas; this regimen improves both overall symptoms and abdominal pain with moderate-quality evidence. 1, 2

• Avoid insoluble fiber such as wheat bran entirely because it consistently aggravates bloating, pain, and overall symptom burden in IBS-C patients. 1, 2

• Provide basic dietary counseling: limit excess caffeine, lactose, fructose, sorbitol, and alcohol; allow adequate time for regular morning defecation. 1, 2

• Consider a 12-week trial of probiotics for global symptoms and abdominal pain, though no specific strain can be recommended; discontinue if no benefit is observed. 1, 2

• Do not recommend IgG antibody-based food elimination diets as they lack supporting evidence and may lead to unnecessary dietary restrictions. 1, 2

• Do not recommend gluten-free diets unless celiac disease has been confirmed by serology and biopsy. 1, 2

Second-Line Therapy: Osmotic Laxatives

• If symptoms persist after 4–6 weeks of fiber therapy, add polyethylene glycol (PEG) and titrate the dose to symptom response; abdominal discomfort is the most common adverse effect. 1, 2

• Re-evaluate efficacy after 3 months of PEG therapy; discontinue if meaningful improvement is not achieved. 1, 2

• A supervised low-FODMAP diet may be considered as second-line dietary therapy when first-line measures fail, but implementation must be supervised by a trained dietitian with structured re-introduction of foods according to tolerance. 1, 2

Third-Line Therapy: Prescription Secretagogues

• Linaclotide 290 mcg once daily on an empty stomach (at least 30 minutes before the first meal) is the preferred prescription agent after failure of first-line therapies; high-quality evidence from trials with over 6,000 participants demonstrates significant benefit for both constipation and abdominal pain. 1, 2, 3

• Linaclotide met FDA response endpoints at 12 weeks with statistically significant improvement in combined responder rates (abdominal pain reduction ≥30% plus ≥3 complete spontaneous bowel movements with increase ≥1 from baseline) compared to placebo: 12–13% vs 3–5%. 3

• 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. 1, 2

• Plecanatide 3 mg daily is an alternative secretagogue with efficacy comparable to linaclotide for patients who cannot tolerate or afford linaclotide. 1, 2

• Lubiprostone 8 mcg twice daily with food is a conditional third-line option for women with IBS-C; moderate-certainty evidence shows modest benefit but nausea occurs in approximately 19% versus 14% with placebo. 1, 2, 3

Management of Persistent Abdominal Pain

• Use peppermint oil as an antispasmodic before escalating to other agents for meal-related abdominal pain; it has a favorable side-effect profile. 1, 2

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

• Tricyclic antidepressants (amitriptyline) are the most effective option for persistent abdominal pain after adequate constipation treatment; start at 10 mg nightly and titrate slowly (by 10 mg per week) to 30–50 mg daily. 1, 2

• Ensure concurrent laxative therapy when prescribing tricyclics to mitigate anticholinergic-induced worsening of constipation. 1, 2

• Continue effective tricyclic antidepressants for at least 6 months before considering discontinuation if the patient reports sustained symptomatic improvement. 1, 2

• Common adverse effects of amitriptyline include dry mouth, visual disturbances, and dizziness; counsel patients about these before initiating therapy. 1, 2

• When tricyclics are not tolerated or exacerbate constipation, selective serotonin reuptake inhibitors (SSRIs) may be considered, although supporting evidence is weaker. 1, 2

Fourth-Line: Psychological Therapies for Refractory Symptoms

• IBS-specific cognitive-behavioral therapy (CBT) and gut-directed hypnotherapy should be offered when symptoms remain refractory after at least 12 months of optimal pharmacologic management; both modalities reduce overall symptom burden. 1, 2

• Prioritize psychological therapies for patients whose symptoms are stress-related, associated with anxiety or depression, or of relatively short duration. 1, 2

Patient Education and Communication

• Explain that IBS-C is a gut-brain interaction disorder with a benign, relapsing-remitting course (not progressive), which reduces patient anxiety and improves adherence. 1, 2

• Introduce the concept of the gut-brain axis and how it is impacted by diet, stress, cognitive, behavioral, and emotional responses to symptoms. 1

• Stress that cure is unlikely, but substantial improvement in symptoms, social functioning, and quality of life is achievable with appropriate management. 1

• Encourage a two-week symptom diary to identify dietary triggers, stressors, and patterns that exacerbate symptoms, thereby guiding treatment choices. 2

Critical Pitfalls to Avoid

• The most critical error is prescribing anticholinergic antispasmodics (dicyclomine, hyoscyamine) for IBS-C based solely on the "IBS" diagnosis without considering the constipation subtype, which will worsen the constipation. 1, 2

• Do not continue docusate (Colace) as it adds no benefit to other laxative therapy and lacks efficacy for constipation. 2

• Do not continue ineffective therapies indefinitely; review treatment efficacy after 3 months and discontinue any therapy that lacks meaningful benefit. 1, 2

• Avoid extensive investigations once an IBS-C diagnosis is established, as unnecessary testing can reinforce illness behavior and delay appropriate treatment. 1, 2

• Do not recommend restrictive dietary interventions, particularly low-FODMAP diet, without intensive dietitian supervision as these may lead to unnecessary dietary restrictions and nutritional deficits. 1, 2