H₂ Antagonists (H₂ Blockers)

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.