Histamines (Histamine Receptors Antagonist/H2 Blockers)

 Histamines (Histamine Receptors Antagonist/H2 Blockers)

They are also called as h2 Antagonists. 

These agents block the action of histamine, thus it reduce the amount of acid released into the stomach. They also promote ulcer healing.

Mechanism of action

They inhibit gastric acid secretion by inhibiting the action of histamine and histamine 2 receptors in gastric parietal cells.

Drug example and doses

1 Cimetidine – 400mg B.D.

2 Ranitidine – 150mg twice daily.

3 Famotidine – 20-40 mg.

4 Nizatidine – 150 mg twice daily.

Indications / Uses


Reflux esophagitis. 


Peptic ulcer. 

Heart burn.

Contraindication / Precautions

Hypersensitivity with this drug. 

Breast feeding women.

Cautiously use in pregnant women.

Adverse effects






Loss of libido due to antiandrogenic Action

Drug interactions

Antacids may inhibit absorption of H2 receptors antagonists.

Cigarette smoking increases gastric acid secretions and May decreases the effectiveness of H2 receptors antagonists.

 Histamines (Histamine Receptors Antagonist/H2 Blockers) Notes PDF

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