What is the appropriate treatment for an adult patient with irritable bowel syndrome with constipation (IBS‑C)?

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

For adult patients with IBS-C, begin with soluble fiber (psyllium 3-4 g/day) and regular exercise, escalate to polyethylene glycol if symptoms persist after 4-6 weeks, then advance to linaclotide 290 mcg daily on an empty stomach as the preferred prescription agent when first-line therapies fail. 1, 2

First-Line Treatment: Lifestyle and Soluble Fiber

• Prescribe regular aerobic physical activity to all IBS-C patients as the foundation of therapy; exercise independently improves global symptom scores and constipation. 1, 2

• Initiate soluble fiber (ispaghula/psyllium) at 3-4 g/day and titrate upward gradually to minimize bloating and gas; this regimen improves both overall IBS-C symptoms and abdominal pain. 1, 2

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

• Provide basic dietary counseling to limit excess caffeine, lactose, fructose, and alcohol, and ensure adequate time for regular defecation. 1

• Consider a 12-week trial of probiotics for global symptoms and bloating; discontinue if no improvement occurs, as no specific strain has demonstrated superior efficacy. 1, 2

Second-Line Treatment: 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. 3, 1

• Re-evaluate efficacy after 3 months of PEG; discontinue if meaningful improvement is not achieved. 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 after failure of first-line therapies; high-quality evidence from two large randomized controlled trials (>1,600 participants) demonstrates significant benefit for both constipation and abdominal pain. 1, 2, 4

• In Trial 1,12% of patients on linaclotide 290 mcg were combined responders (≥30% abdominal pain reduction plus ≥3 CSBMs with ≥1 CSBM increase) for at least 9 out of 12 weeks versus 5% on placebo (treatment difference 7%, 95% CI 3.2-10.9%). 4

• In Trial 2,13% of patients on linaclotide were combined responders versus 3% on placebo (treatment difference 10%, 95% CI 6.1-13.4%). 4

• Diarrhea is the most common adverse event with linaclotide, occurring as the mechanism of action; counsel patients about this risk before initiating therapy. 1, 4

• Review efficacy after 3 months and discontinue linaclotide if no response. 1

• Tenapanor is an alternative FDA-approved secretagogue for IBS-C in adults. 5

• 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 a higher rate of nausea (≈19% vs 14% with placebo). 1, 2

Management of Persistent Abdominal Pain

• For meal-related abdominal pain, use peppermint oil as an antispasmodic before escalating to other agents; 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 worsen constipation. 1, 2

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

• When prescribing tricyclics for IBS-C, ensure concurrent adequate laxative therapy is in place to mitigate anticholinergic-induced constipation. 1, 2

• Continue tricyclics for at least 6 months if the patient experiences symptomatic improvement. 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: Supervised Dietary Therapy

• If symptoms persist despite pharmacologic therapy, refer to a trained dietitian for a supervised low-FODMAP diet delivered in three phases: (1) restriction (4-6 weeks), (2) systematic re-introduction, and (3) personalized maintenance based on individual tolerance. 1, 2

• During the re-introduction phase, FODMAPs should be added back according to the patient's tolerance to avoid unnecessary long-term restriction. 2

Fifth-Line: Psychological Therapies for Refractory Symptoms

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

• These brain-gut behavior therapies are specifically designed for IBS and differ from psychological therapies that target depression and anxiety alone. 2

Critical Pitfalls to Avoid

• Do NOT prescribe anticholinergic antispasmodics (dicyclomine, hyoscyamine) in IBS-C based solely on the "IBS" diagnosis without considering the constipation subtype; this is the critical error that will worsen the constipation. 1, 2

• Do NOT continue docusate (Colace) as it adds no benefit to other laxative therapy. 1

• Do NOT recommend IgG-based food elimination diets or gluten-free diets unless celiac disease is confirmed; current evidence does not support their use in IBS-C and may lead to unnecessary dietary restrictions. 1, 2, 6

• Avoid extensive investigations once an IBS-C diagnosis is established in patients <45 years without alarm features (unintentional weight loss ≥5%, rectal bleeding, anemia, fever, nocturnal symptoms, family history of colorectal cancer or inflammatory bowel disease), as unnecessary testing reinforces illness anxiety. 1, 2

• Review treatment efficacy after 3 months and discontinue any therapy that lacks meaningful benefit. 1, 2