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Classification of Drugs Used in Irritable Bowel Syndrome (IBS)

Irritable Bowel Syndrome (IBS) is a chronic gastrointestinal disorder characterized by abdominal pain, bloating, and altered bowel habits. Treatment options focus on symptom relief, and include various drug classes to target diarrhea, constipation, and pain.

1. Antispasmodics

  • Examples: Hyoscine, Dicyclomine
  • Mechanism of Action: Inhibits acetylcholine at muscarinic receptors in the GI tract, reducing smooth muscle spasms and abdominal pain.
  • Adverse Effects: Dry mouth, blurred vision, constipation, dizziness
  • Contraindications: Glaucoma, urinary retention, myasthenia gravis

2. Antidiarrheal Agents

  • Examples: Loperamide, Diphenoxylate
  • Mechanism of Action: Slows intestinal motility, increases water absorption, and reduces diarrhea.
  • Adverse Effects: Constipation, abdominal pain, dizziness, nausea
  • Contraindications: Severe colitis, toxic megacolon

3. Laxatives (for IBS with Constipation)

  • Examples: Polyethylene glycol, Lactulose
  • Mechanism of Action: Osmotic action retains water in stool, softening it and promoting bowel movements.
  • Adverse Effects: Diarrhea, bloating, abdominal cramps
  • Contraindications: Bowel obstruction, dehydration

4. Selective Serotonin Receptor Agonists (5-HT4 Agonists)

  • Examples: Prucalopride, Tegaserod
  • Mechanism of Action: Stimulates serotonin receptors in GI tract, promoting motility and relieving constipation.
  • Adverse Effects: Headache, nausea, diarrhea, abdominal pain
  • Contraindications: Cardiovascular diseases, severe renal impairment

5. Guanylate Cyclase-C Agonists

  • Examples: Linaclotide, Plecanatide
  • Mechanism of Action: Increases cyclic GMP, stimulating intestinal fluid secretion and enhancing motility.
  • Adverse Effects: Diarrhea, abdominal pain, bloating
  • Contraindications: GI obstruction, children under 6 years

6. Rifamycin Antibiotics

  • Examples: Rifaximin
  • Mechanism of Action: Reduces gut bacteria, potentially relieving symptoms like bloating and discomfort.
  • Adverse Effects: Nausea, dizziness, headache
  • Contraindications: Hypersensitivity to rifamycins

7. Tricyclic Antidepressants (TCAs) and SSRIs

  • Examples: Amitriptyline (TCA), Fluoxetine (SSRI)
  • Mechanism of Action: Modulates pain perception in the central nervous system and reduces GI spasms due to anticholinergic effects.
  • Adverse Effects: Dry mouth, drowsiness, constipation (TCAs), sexual dysfunction (SSRIs)
  • Contraindications: Glaucoma, heart disease, severe depression (for TCAs)

8. Probiotics

  • Examples: Lactobacillus, Bifidobacterium
  • Mechanism of Action: Helps restore gut microbiota balance, potentially reducing symptoms like bloating and irregular bowel movements.
  • Adverse Effects: Gas, bloating
  • Contraindications: Severe immunocompromised states
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