Irritable Bowel Syndrome Study Notes

Irritable Bowel Syndrome (IBS)

Pharmacotherapy of Gastrointestinal Diseases

Definition of IBS

  • Also Known As: Spastic, nervous, or irritable colon.

  • Definition: Irritable bowel syndrome (IBS) is a functional gastrointestinal disorder characterized by abdominal pain and altered bowel habits in the absence of any organic cause.

  • Prevalence: IBS is a highly prevalent chronic disorder that significantly reduces patients' quality of life.

Pathophysiology of IBS

  • Mechanisms: Although the exact pathophysiologic abnormalities with IBS are still being actively investigated, IBS likely results from altered visceral and motor dysfunction of the intestine from a variety of causes. Key mechanisms that contribute to IBS include:

    • Alteration in intestinal motility (motor dysfunction): Changes in the frequency and regularity of intestinal contractions. Fast motility can lead to diarrhea, while slow motility can cause constipation.

    • Visceral hypersensitivity: Increased sensation in response to intestinal activity due to abnormal central nervous system (CNS) processing of afferent signals.

    • Brain-gut axis dysregulation: Alteration in communications between the enteric nervous system and CNS.

    • Altered mucosal permeability and immune function.

    • Altered gut microbiota: This can include intestinal bacterial overgrowth.

    • Bile acid malabsorption.

Risk Factors for IBS

  • Demographics:

    • Young Age: More common in individuals under age 50.

    • Female Gender: More prevalent in women; estrogen therapy can be a risk factor.

  • Genetic Factors: Family history of IBS.

  • Psychological Factors: Stress and mental health issues such as anxiety and depression; history of physical or emotional abuse.

  • Others: Food allergies or intolerances, post-infectious IBS (after severe gastroenteritis), certain medications (including antibiotics and NSAIDs).

Clinical Presentation and Diagnosis of IBS

  • Presentation: Can manifest as diarrhea, constipation, or alternating patterns; includes lower abdominal pain, disturbed defecation, and bloating in the absence of structural or biochemical factors.

  • Diagnosis: Mainly symptom-based, as there's no definitive test for IBS.

    • Rome IV Criteria for IBS: Recurrent abdominal pain, on average ≥1 day/week in the past three months, related to at least two of the following:

      • Relieved with defecation.

      • Onset associated with changes in stool frequency.

      • Onset associated with changes in stool form (appearance).

    • Criteria must be met for the past three months with symptom onset occurring at least six months prior.

  • Diagnostic Tests: Useful lab tests include CBC, metabolic panel, C-reactive protein, thyroid profile (if indicated), tests for celiac disease, stool sample evaluation, colonoscopy (case-dependently).

Alarming Symptoms

  • Signs that warrant further investigation:

    • Age ≥50 years with no previous colon cancer screening.

    • Recent change in bowel habit.

    • Overt gastrointestinal bleeding.

    • Nocturnal pain or stool passage.

    • Unintentional weight loss.

    • Family history of colorectal cancer or inflammatory bowel disease.

    • Palpable abdominal mass or lymphadenopathy.

    • Evidence of iron-deficiency anemia on testing.

    • Positive test for fecal occult blood.

Treatment of IBS

Nonpharmacologic Treatment

  • Lifestyle Modifications:

    1. Dietary Modification: Careful dietary history may reveal symptoms related to specific foods; may include low FODMAP diet.

    2. Education and Reassurance: Exclude gas-producing foods (e.g., beans, onions, gluten).

    3. Regular Exercise.

    4. Stress Reduction.

    5. Avoid Sleep Deprivation.

    6. Psychological Treatment: Options include psychotherapy, relaxation therapy, hypnotherapy, cognitive behavioral therapy (CBT).

Pharmacologic Treatment for IBS

  • General: Treatment needed for moderate to severe symptoms impairing quality of life. Must be based on predominant symptoms and subtype.

  • Treatment often involves pharmacologic interventions to control flare-ups or continuous therapy for extended periods.

  • Incremental Changes in Therapy: Adjustments can occur at two- to four-week intervals.

  • Pharmacologic Classes:

    1. Antispasmodics: (e.g., hyoscine, dicyclomine, peppermint oil, mebeverine)

      • Mechanism: Reduce abdominal pain by decreasing smooth muscle contraction.

      • Side Effects: May include dry mouth, dizziness, blurred vision, constipation.

    2. Tricyclic Antidepressants (TCA): (e.g., amitriptyline, nortriptyline)

      • Mechanism: Modulate pain through neurotransmitter reuptake effects.

      • Benefits: Help reduce abdominal pain and diarrhea; side effects may include constipation, sedation.

    3. Selective Serotonin Reuptake Inhibitors (SSRI): (e.g., fluoxetine, paroxetine)

      • Potential to improve symptoms; studies show conflicting results regarding efficacy in IBS.

    4. Probiotics: Show some evidence for improving global IBS symptoms.

    5. IBS-C Specific Treatments:

      • Laxatives such as magnesium hydroxide, sorbitol, or polyethylene glycol (PEG).

      • Linaclotide: A guanylate cyclase agonist; recommended dose is 290 micrograms daily.

      • Tenapanor: Approved for IBS-C; dosage is 50 mg twice daily.

      • Tegaserod: 5-HT4 receptor partial agonist; approved for women under 65 with no cardiovascular history.

    6. IBS-D Specific Treatments:

      • Antimotility Agents: (e.g., loperamide, eluxadoline)

        • Loperamide: Dosage of 2 mg 45 minutes before meals, max 16 mg/day.

      • Bile Acid Sequestrants: (e.g., cholestyramine, colestipol)

        • Considered based on bile acid malabsorption effects.

      • Serotonin Antagonists: (e.g., alosetron); targeted at women with severe symptoms.

      • Antibiotics: (e.g., rifaximin); indicated for treating IBS-D and small intestinal bacterial overgrowth.