Irritable Bowel Syndrome (IBS)

Irritable Bowel Syndrome (IBS)

• IBS is a functional bowel disorder (FBD) characterized by recurrent abdominal pain associated with defecation or a change in bowel habits.
• IBS involves abdominal pain and bloating associated with a change in bowel habits.

Classification of IBS

• IBS is classified into three types:
  • Constipation predominant (IBS-C)
  • Diarrhea predominant (IBS-D)
  • Mixed with both constipation and diarrhea (IBS-M)

Pathophysiology of IBS

• IBS is thought to result from dysregulation of the "brain–gut axis"
• Enteric nerves control intestinal smooth muscle action and are connected to the brain by the autonomic nervous system
• Several neurochemicals mediate their function, including serotonin (5-HT), acetylcholine, substance P, and nitric oxide
• Serotonin is particularly important as the GI tract contains the largest amounts in the body

Role of 5-HT in IBS

• Two 5-HT receptor subtypes, 5-HT3 and 5-HT4, are involved in gut motility, visceral sensitivity, and gut secretion
• 5-HT3 receptors slow colonic transit and increase fluid absorption
• 5-HT4 receptor stimulation accelerates colonic transit

Other Factors Contributing to IBS

• Some IBS patients demonstrate sensitivity to common foods such as wheat, beef, soy, and eggs
• Evidence suggests that an immune component may be involved in IBS patients

Treatment of IBS

Agents for Constipation Predominance (IBS-C)

• Bulk producers: psyllium may increase flatulence, while methylcellulose products are less likely to increase gas production
• Osmotic laxatives: polyethylene glycol 3350 (PEG) or PEG 3350 with electrolytes
• Linaclotide relieves abdominal pain, bloating, and constipation associated with IBS-C
• Lubiprostone treats IBS-C, but only in women aged 18 years and older

Agents for Diarrhea Predominance (IBS-D)

• Loperamide inhibits peristalsis and fluid secretion
• Antispasmodics: dicyclomine and hyoscyamine have been used to treat abdominal pain in IBS patients

Antidepressants in IBS

• Tricyclic antidepressants (TCAs) may help abdominal pain in IBS-D
• Selective serotonin-reuptake inhibitors (SSRIs) may be useful in IBS-C

Rifaximin in IBS

• Rifaximin is a semisynthetic antibacterial agent that inhibits bacterial overgrowth, which contributes to bloating
• It should be used with caution in patients with severe hepatic impairment

Clinical Presentation and Diagnosis of IBS

• Diagnosis is based on symptoms, absence of alarm symptoms, and exclusion of organic disease
• Barium enema, sigmoidoscopy, or colonoscopy may be indicated in the presence of red flag symptoms

Treatment Goals and Approach

• Goals of therapy include complete relief of symptoms and improving quality of life
• Treatment is based on the predominant symptoms of the patient
• For constipation-predominant symptoms (IBS-C), increased dietary fiber is considered first-line therapy