GI Pharmacology Learning Objectives

Question 1

What is the importance of understanding the pathophysiology of GI disorders in pharmacology?

Answer 1

• Provides context for pharmacological interventions
• Helps select appropriate drug therapy
• Predicts potential side effects and treatment outcomes

Question 2

What are the main classes of drugs used to treat gastrointestinal disorders?

Answer 2

• Antiemetics (e.g., H1 blockers, D2 antagonists, 5-HT3 antagonists, NK1 antagonists)
• Acid suppressants (e.g., antacids, H2 blockers, PPIs)
• Cytoprotective agents (e.g., misoprostol, sucralfate)
• Laxatives (e.g., osmotic, stimulant, bulk-forming)
• Antidiarrheals (e.g., loperamide, methylnaltrexone)
• Prokinetics (e.g., metoclopramide, domperidone)
• Spasmolytics (e.g., hyoscine butylbromide)
• Antibiotics (e.g., for H. pylori eradication)

Question 3

What is the rationale for using each drug class in GI disorders?

Answer 3

• **Antiemetics: **Block neurotransmitters involved in vomiting
• Acid suppressants: Reduce acid to promote healing in ulcers or GORD
• Cytoprotectives: Enhance mucosal defense against acid
• Laxatives: Restore bowel movement in constipation
• Antidiarrheals: Slow gut motility and promote fluid reabsorption
• Prokinetics: Improve gastric emptying
• **Spasmolytics: **Relieve smooth muscle spasm
• **Antibiotics: **Eradicate causative organisms like H. pylori

Question 4

What are the mechanisms of action of the key GI drug classes?

Answer 4

• H1/M1 blockers: Inhibit vestibular input to vomiting centre
• D2 antagonists: Block CTZ and enhance motility
• 5-HT3 antagonists: Block serotonin at CTZ and gut
• PPIs: Irreversibly inhibit H⁺/K⁺ ATPase in parietal cells
• H2 blockers: Competitively inhibit histamine at H2 receptors
• **Misoprostol: **EP3 receptor agonist → ↑ mucus, ↓ acid
• Sucralfate: Forms protective barrier over ulcers
• **Laxatives: **Varying mechanisms (bulk-forming, osmotic, stimulant)
• Loperamide: μ-opioid agonist → ↓ peristalsis
• Methylnaltrexone: μ-opioid antagonist in GI only
• Domperidone/Metoclopramide: D2 antagonism → ↑ motility

Question 5

How is the GI tract regulated by the enteric and autonomic nervous systems?

Answer 5

Enteric Nervous System (ENS)
Intrinsic control of GI motility, secretion, and blood flow; contains sensory and motor neurons

Autonomic Nervous System (ANS)
Parasympathetic: Stimulates GI activity (“rest and digest”)
Sympathetic: Inhibits GI function (“fight or flight”)