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

Treatment of Constipation-Predominant IBS (IBS-C)

Start with soluble fiber supplementation (psyllium/ispaghula) at 3-4 g/day, gradually titrating upward, and if symptoms persist after 4-6 weeks, escalate to prescription secretagogues like linaclotide as the most effective second-line agent, while reserving tricyclic antidepressants for refractory abdominal pain. 1, 2

First-Line Treatment: Lifestyle and Dietary Interventions

Soluble fiber is the cornerstone of initial therapy for IBS-C. The 2021 American College of Gastroenterology Guidelines made a strong recommendation specifically for soluble fiber (not insoluble fiber) based on systematic review of 15 RCTs showing benefit with minimal adverse effects. 1 Start with low doses of 3-4 g/day of psyllium or ispaghula and build up gradually to avoid bloating and gas—this slow titration is critical to tolerability. 1, 2 Recent meta-analysis data confirm that doses >10 g/day and treatment duration of at least 4 weeks are optimal for improving stool frequency and consistency. 3

Critically, avoid insoluble fiber (wheat bran, whole grains) as it consistently exacerbates bloating and abdominal pain in IBS-C patients. 1

Regular physical exercise should be recommended to all IBS-C patients as foundational therapy, providing significant benefits for global symptom management. 2

Low FODMAP Diet as Second-Line Dietary Therapy

If soluble fiber fails after an adequate trial (4-6 weeks), consider a low FODMAP diet (LFD) as second-line dietary intervention. 1, 2 The LFD was found to be the most effective diet strategy for relief of global symptoms, abdominal pain, and bloating in a network meta-analysis of 13 RCTs. 1 However, this must be supervised by a trained registered dietitian and implemented in three phases: restriction (lasting no more than 4-6 weeks), reintroduction of FODMAP foods, and personalization based on tolerance. 1 The evidence specifically for IBS-C is weaker than for other IBS subtypes, but patients with IBS-C have shown benefit from higher soluble fiber intake within this framework. 1

Important caveat: Screen patients for eating disorder risk using tools like SCOFF questionnaire before recommending restrictive diets, as the LFD may induce detrimental changes to gut microbiota and promote overly restrictive eating habits. 1

Second-Line Treatment: Osmotic Laxatives and Secretagogues

When dietary interventions prove insufficient, escalate to pharmacological therapy:

Polyethylene glycol (PEG) is an effective osmotic laxative for constipation, with dose titrated according to symptoms; abdominal pain is the most common side effect. 2

Lubiprostone (24 mcg twice daily with food) is FDA-approved for IBS-C in women ≥18 years old and acts as a chloride channel activator to increase intestinal fluid secretion. 4, 5 Take with food and water to reduce nausea, which is the most common adverse effect. 4 Diarrhea may occur and patients should discontinue if severe diarrhea develops. 4

Linaclotide is the most effective secretagogue available for IBS-C and should be the preferred second-line agent when first-line therapies fail, based on strong recommendation and high-quality evidence. 2, 5 It is a guanylate cyclase-C agonist that improves both constipation and abdominal pain. 5 Diarrhea is a common side effect but is generally manageable. 2

Plecanatide and tenapanor are additional FDA-approved options that are generally well tolerated and efficacious in improving both constipation and abdominal pain in IBS-C. 5

Third-Line Treatment: Antispasmodics and Neuromodulators

For persistent abdominal pain despite adequate laxative therapy, tricyclic antidepressants (TCAs) are the most effective option. 2 Start amitriptyline at 10 mg once daily at bedtime and titrate slowly (by 10 mg/week) to 30-50 mg daily. 1, 2 Continue for at least 6 months if symptomatic response occurs. 1, 2

Critical pitfall: TCAs may worsen constipation through anticholinergic effects, so ensure adequate laxative therapy is in place before initiating and use cautiously in IBS-C. 2 If TCAs worsen constipation or are not tolerated, SSRIs may be effective as alternative neuromodulators for global symptoms. 2

Certain antispasmodics with anticholinergic properties (like dicyclomine) can be effective for abdominal pain and global symptoms, but avoid anticholinergic antispasmodics in IBS-C patients as their mechanism of reducing intestinal motility can exacerbate constipation. 2 Direct smooth muscle relaxants like peppermint oil may be useful alternatives for pain without worsening constipation. 1, 2

Fourth-Line Treatment: Psychological Therapies

For symptoms persisting despite 12 months of pharmacological treatment, consider IBS-specific cognitive behavioral therapy (CBT) or gut-directed hypnotherapy. 1, 2 These brain-gut behavioral therapies are specifically designed for IBS and differ from psychological therapies targeting depression and anxiety alone. 2 They are effective for global symptoms with strong recommendation, though quality of evidence is low. 2

Refer to a gastropsychologist if IBS symptoms or their impact are moderate to severe, the patient accepts that symptoms relate to gut-brain dysregulation, and has time to devote to learning new coping strategies. 2

Treatment Monitoring and Common Pitfalls

Review treatment efficacy after 3 months and discontinue ineffective medications. 1, 2 TCAs should be continued for at least 6 months if symptomatic response occurs. 1

Critical errors to avoid:

• Prescribing anticholinergic antispasmodics for IBS-C based solely on "IBS" diagnosis without considering the constipation subtype—this worsens constipation. 2
• Using IgG antibody-based food elimination diets, which lack evidence and lead to unnecessary dietary restrictions. 1, 2
• Recommending gluten-free diets unless celiac disease is confirmed. 1, 2
• Performing extensive testing once IBS-C diagnosis is established. 2

Recognize that IBS is a disorder of gut-brain interaction requiring explanation of the gut-brain axis to patients, and symptoms may relapse and remit over time, requiring periodic adjustment of treatment strategy. 2 Managing patient expectations is crucial, as complete symptom resolution is often not achievable—the goal is symptom relief and improved quality of life. 2