What is the first line treatment for a patient with irritable bowel syndrome (IBS)?

First-Line Treatment for Irritable Bowel Syndrome

Begin with lifestyle modifications—specifically regular physical exercise and soluble fiber supplementation (ispaghula/psyllium 3-4 g/day, gradually increased)—as these form the foundation of IBS treatment with strong evidence for improving global symptoms and abdominal pain. 1, 2

Foundational Lifestyle Interventions (Start Here for All Patients)

• Recommend regular physical exercise to all IBS patients as this improves global symptoms and should be the basis of treatment. 1, 2

• Provide first-line dietary counseling focusing on regular meal patterns, adequate hydration (6-8 glasses of water daily), and limiting caffeine, alcohol, and gas-producing foods (beans, onions, celery, carrots, Brussels sprouts). 2

• Start soluble fiber supplementation with ispaghula (psyllium) at 3-4 g/day, building up gradually over 2-4 weeks to avoid bloating and gas—this is effective for both global symptoms and abdominal pain. 3, 1, 2

• Avoid insoluble fiber (wheat bran) entirely as it consistently worsens IBS symptoms, particularly bloating. 1, 2

First-Line Pharmacological Treatment by Symptom Pattern

For Abdominal Pain and Bloating

• Consider antispasmodics with anticholinergic properties (such as dicyclomine 40 mg four times daily) for abdominal pain and global symptoms, particularly when symptoms are exacerbated by meals. 3, 2, 4 In FDA trials, 82% of patients treated with dicyclomine showed favorable response versus 55% with placebo. 4

• Warn patients about common side effects: dry mouth, visual disturbance, and dizziness. 3, 2

• Peppermint oil can be used as an alternative antispasmodic with fewer side effects. 1

For IBS with Diarrhea (IBS-D)

• Loperamide 2-4 mg up to four times daily reduces stool frequency, urgency, and fecal soiling. 3, 1, 2 Titrate carefully to avoid abdominal pain, bloating, nausea, and constipation. 3

For IBS with Constipation (IBS-C)

• Begin with soluble fiber (ispaghula) at 3-4 g/day, increasing gradually. 1, 2

• If fiber fails after 4-6 weeks, add polyethylene glycol (osmotic laxative), titrating the dose according to symptoms. 1

• Critical pitfall: Do NOT use anticholinergic antispasmodics like dicyclomine in IBS-C patients, as they reduce intestinal motility and enhance water reabsorption, which will worsen constipation. 1

Probiotics as First-Line Option

• Consider a 12-week trial of probiotics for global symptoms and abdominal pain, though no specific species or strain can be recommended; discontinue if no improvement occurs. 3, 1, 2 This recommendation is weak due to very low quality evidence, but probiotics are safe and patients often request them. 3

Second-Line Dietary Therapy (If First-Line Fails After 4-6 Weeks)

• A low-FODMAP diet is effective for global symptoms and abdominal pain, but must be supervised by a trained dietitian with planned reintroduction of foods according to tolerance. 3, 1, 2 This is a second-line dietary therapy, not first-line. 3

• Do NOT recommend gluten-free diets unless celiac disease has been confirmed with serological testing, as evidence does not support their use in IBS. 3, 1, 2

• Never use IgG antibody-based food elimination diets as they lack evidence and may lead to unnecessary dietary restrictions. 1, 2

When to Escalate to Second-Line Pharmacotherapy

• If symptoms persist after 12 weeks of first-line therapies, escalate to tricyclic antidepressants (TCAs) starting with amitriptyline 10 mg once daily at bedtime, titrated slowly (by 10 mg/week) to 30-50 mg daily. 3, 1, 2 This is the most effective second-line treatment for global symptoms and abdominal pain with strong recommendation and moderate quality evidence. 3

• Provide careful explanation that TCAs are used as gut-brain neuromodulators to modulate pain perception through the brain-gut axis, not for depression. 3, 2

• Counsel about side effects: dry mouth, drowsiness, and constipation (particularly problematic in IBS-C). 2

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

Critical Pitfalls to Avoid

• Never start with insoluble fiber (wheat bran) as it will worsen symptoms, particularly bloating. 1, 2

• Do not perform extensive investigations once IBS is diagnosed based on Rome criteria in the absence of alarm features (rectal bleeding, unintentional weight loss, family history of colon cancer, anemia, nocturnal symptoms). 1, 2

• Do not promise complete symptom resolution; the goal is symptom relief and improved quality of life, not cure. 2

• Review treatment efficacy after 3 months and discontinue if no response. 1, 2

When to Refer to Gastroenterology

• Refer when there is diagnostic doubt, severe symptoms, or symptoms refractory to first-line treatments after 12 weeks. 2

• Consider psychological therapies (IBS-specific cognitive behavioral therapy or gut-directed hypnotherapy) when symptoms persist despite 12 months of pharmacological treatment. 3, 1, 2