Pharmacology of GIT

 Pharmacology of the Gastrointestinal Tract (GIT)

GIT pharmacology includes drugs used to manage disorders like acid reflux, ulcers, constipation, diarrhea, vomiting, and inflammatory diseases.

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🔹 1. Antacids

Use: Neutralize stomach acid (quick relief).

Examples:

Aluminum hydroxide

Magnesium hydroxide

Calcium carbonate

Side Effects:

Aluminum → constipation

Magnesium → diarrhea

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🔹 2. H₂-Receptor Blockers

Use: Reduce acid secretion.

Mechanism: Block histamine H₂-receptors on parietal cells.

Examples:

Ranitidine (withdrawn in many countries)

Famotidine

Cimetidine

Use in: GERD, peptic ulcer

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🔹 3. Proton Pump Inhibitors (PPIs)

Use: Most potent acid suppressors.

Mechanism: Inhibit H⁺/K⁺ ATPase pump in gastric parietal cells.

Examples:

Omeprazole

Pantoprazole

Esomeprazole

Side Effects: Long-term use → B12 deficiency, osteoporosis.

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🔹 4. Anti-Helicobacter pylori Drugs

Use: Eradicate H. pylori in peptic ulcer.

Triple Therapy:

PPI + Clarithromycin + Amoxicillin or Metronidazole

Quadruple Therapy: Add bismuth subsalicylate.

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🔹 5. Antiemetics (For Vomiting/Nausea)

a. Dopamine (D₂) Antagonists

Examples: Metoclopramide, Domperidone

Use: Nausea, GERD

Side Effects: Extrapyramidal symptoms

b. 5-HT₃ Antagonists

Examples: Ondansetron, Granisetron

Use: Chemo-induced nausea, post-op nausea

c. Antihistamines (H₁ blockers)

Examples: Promethazine, Cyclizine

Use: Motion sickness

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🔹 6. Laxatives (For Constipation)

a. Bulk-forming

Examples: Psyllium, Methylcellulose

b. Osmotic

Examples: Lactulose, Magnesium citrate

c. Stimulant

Examples: Senna, Bisacodyl

d. Stool softeners

Examples: Docusate sodium

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🔹 7. Antidiarrheal Agents

a. Opioid Agonists

Examples: Loperamide, Diphenoxylate

Mechanism: Decrease gut motility

b. Adsorbents

Examples: Activated charcoal, kaolin

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🔹 8. Anti-inflammatory Drugs (for IBD)

a. Aminosalicylates

Examples: Sulfasalazine, Mesalazine

b. Corticosteroids

Examples: Prednisone, Budesonide

c. Immunosuppressants

Examples: Azathioprine, Methotrexate

d. Biologics

Examples: Infliximab (anti-TNF)

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🔹 9. Prokinetic Agents

Use: Enhance gut motility.

Examples: Metoclopramide, Cisapride (limited use)

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🔹 10. Drugs for Bile Disorders

Ursodeoxycholic acid: Dissolves gallstones, used in cholestasis.

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