What is the initial treatment for irritable bowel syndrome?

Initial Treatment for Irritable Bowel Syndrome

Begin with regular physical exercise and soluble fiber (ispaghula/psyllium) 3-4 g/day as foundational first-line therapy for all IBS patients, regardless of subtype. 1, 2

Foundational Lifestyle Interventions (Start Here for All Patients)

• Recommend regular physical exercise to every IBS patient as this improves global symptoms and forms the foundation of treatment. 1, 2

• Provide basic dietary counseling focusing on regular meal patterns, adequate hydration (not excessive), limiting caffeine and alcohol, and allowing adequate time for regular defecation. 3, 1, 2

• Completely avoid insoluble fiber (wheat bran) as it consistently worsens IBS symptoms, particularly bloating, across all subtypes. 1, 2

First-Line Pharmacological Treatment

For All IBS Subtypes (Global Symptoms and Abdominal Pain)

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

• Consider antispasmodics with anticholinergic properties (such as dicyclomine taken before meals) for abdominal pain and global symptoms, but counsel patients about dry mouth, visual disturbances, and dizziness. 3, 1, 2

• Peppermint oil provides an alternative antispasmodic effect with a more favorable side-effect profile than anticholinergics. 3, 1

• Trial probiotics for 12 weeks for global symptoms and abdominal pain, though no specific species or strain can be recommended; discontinue if no improvement occurs. 1, 2

For IBS with Diarrhea (IBS-D)

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

For IBS with Constipation (IBS-C)

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

• Add polyethylene glycol (osmotic laxative) if fiber fails after 4-6 weeks, titrating the dose according to symptoms; abdominal pain is the most common side effect. 1, 2

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 after 4-6 weeks of strict restriction. 1, 2, 4

• Never recommend gluten-free diets unless celiac disease has been confirmed, as evidence does not support their use in IBS. 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 (After 12 Weeks of First-Line Failure)

• Tricyclic antidepressants (TCAs) are the most effective second-line treatment for global symptoms and abdominal pain across all IBS subtypes; start amitriptyline 10 mg once daily at bedtime, titrate slowly by 10 mg/week to 30-50 mg daily, and continue for at least 6 months if symptomatic response occurs. 3, 1, 2

• Provide careful explanation that TCAs are used as gut-brain neuromodulators, not for depression, and counsel about side effects including dry mouth, drowsiness, and constipation (particularly problematic in IBS-C). 1, 2

• SSRIs are effective alternatives when TCAs are not tolerated, particularly if TCAs worsen constipation in IBS-C patients. 1, 2

Additional Second-Line Options for IBS-D

• 5-HT3 receptor antagonists (such as alosetron) are highly efficacious second-line drugs for IBS-D, though alosetron carries a boxed warning for ischemic colitis (0.2% through 3 months) and complications of constipation, and is only available through a restricted prescribing program. 1, 5, 6

• Rifaximin (non-absorbable antibiotic) is effective for IBS-D, with 47% of patients achieving response in abdominal pain and stool consistency versus 36-39% with placebo, though its effect on abdominal pain alone is limited. 1, 5, 7

When to Refer to Gastroenterology

• Refer when there is diagnostic doubt, presence of alarm features (weight loss, rectal bleeding, family history of IBD or celiac disease), severe symptoms, or symptoms refractory to first-line treatments after 12 weeks. 1, 2

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

Critical Pitfalls to Avoid

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

• Avoid extensive investigations once IBS is diagnosed based on symptom criteria in the absence of alarm features. 1, 2

• Do not promise complete symptom resolution; the goal is symptom relief and improved quality of life. 1, 2

• Review treatment efficacy after 3 months and discontinue ineffective therapies. 3, 1

• Recognize that the low-FODMAP diet should only be strict for 4-6 weeks initially, as long-term strict restriction may negatively impact intestinal microbiome; reintroduction under dietitian guidance is essential. 1, 4, 8