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H₂ Antagonists (H₂ Blockers)

1 min read

Definition of H₂ Antagonists (H₂ Blockers)

  • H₂ antagonists (H₂ Blockers) are a class of drugs that block histamine H₂ receptors located on the parietal cells of the stomach.

  • By inhibiting histamine's action, these drugs reduce the production of stomach acid.

Medical Uses:

  • Gastroesophageal Reflux Disease (GERD)

  • Dyspepsia

  • Peptic Ulcers (Gastric and Duodenal)

  • Stress Ulcers

  • Prevention of Aspiration Pneumonitis During Surgery

Side Effects:

  • Blurred vision

  • Hypotension

  • Headache

  • Tiredness

  • Dizziness

  • Diarrhea

  • Constipation

  • Rash

Mechanism of Action:

  1. Histamine Binding: Under normal conditions, histamine binds to H₂ receptors on parietal cells.

  2. Signal Transduction: H₂ receptors, which are G-protein coupled receptors, activate the cAMP pathway.

  3. Proton Pump Activation: Increased cAMP levels elevate intracellular Ca²⁺, activating the proton pump (H⁺/K⁺-ATPase), leading to increased H⁺ secretion and hydrochloric acid (HCl) production.

  4. Blockade by H₂ Antagonists: These drugs inhibit H₂ receptors, preventing histamine binding. This suppression halts the downstream signaling, reducing proton pump activity and decreasing HCl secretion.


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