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Introduction
H₂ antagonists, sometimes referred to as H2RAs andand also called H₂ blockers, are a class of medications that block the action of histamine at the histamine H₂ receptors of the parietal cells in the stomach. This decreases the production of stomach acid.
H₂ antagonists, sometimes referred to as H2RAs andand also called H₂ blockers, are a class of medications that block the action of histamine at the histamine H₂ receptors of the parietal cells in the stomach. This decreases the production of stomach acid.
History
History
• 1970s: Developed by Sir James Black at Smith, Kline & French to block histamine at H2 receptors in the stomach.
• 1976: Cimetidine (Tagamet) became the first approved H2 blocker, revolutionizing treatment of ulcers and acid reflux.
• 1980s–1990s: Safer and more effective drugs like Ranitidine (Zantac) and Famotidine (Pepcid) were introduced.
• 2020: Ranitidine was recalled by the FDA due to contamination with NDMA, a possible carcinogen.
• Though now less used than PPIs, H2 blockers remain important for mild acid disorders or patients intolerant to PPIs.
MOA
MOA
Watch this short video to understand the Mechanism of Action of H2 Receptor Blockers:
Watch this short video to understand the Mechanism of Action of H2 Receptor Blockers:
H2 receptor blockers (or H2 receptor antagonists) work by blocking histamine H2 receptors on the parietal cells in the stomach lining.
Examples of Medication
Zantac ( Ranitidine )
Roxagen ( Roxatidine )
Nizatect ( Nizatidine )
Cimetidine (Cimetidine)
Famotin ( Famotidine )
Indications
H2 receptor blockers are primarily used to reduce gastric acid secretion. They are indicated in the following clinical conditions:
Peptic Ulcer Disease (PUD) :
Helps in healing gastric and duodenal ulcers by reducing acid production.
Zollinger-Ellison Syndrome :
A rare condition involving gastrin-secreting tumors that cause excessive acid production.
Gastroesophageal Reflux Disease (GERD) :
Relieves symptoms of heartburn and acid regurgitation by lowering gastric acidity.
Stress Ulcer Prophylaxis :
(In hospitalized patients),
To prevent stress-related mucosal damage in critically ill patients.
Side effects
Precautions
&
Contraindications
There are currently no absolute contraindications to H2RA therapy. However, these drugs should not be used in patients with known hypersensitivity to any H2RA or formulation components.
Cross-sensitivity has been reported. Patients should stop using OTC H2RAs if they experience difficulty or pain when swallowing, vomiting with blood, or bloody or black stools. These patients should seek immediate medical attention.
Prior recalls of ranitidine: The FDA recalled ranitidine tablets due to unacceptable levels of N-nitrosodimethylamine (NDMA), a potential carcinogen.
Monographs
DOC-20250324-WA0056..pdfعبد الفتاح 3.pdffinallll.docx_20250324_232824_٠٠٠٠.pdfنشاط فارما (1).pdfDrug monograph Ziad Nadeem.pdfReferences
1. Katzung, B. G., & Trevor, A. J. (2021). Basic and Clinical Pharmacology (15th ed.). McGraw Hill Education.
2. National Institutes of Health (NIH). MedlinePlus: H2 Blockers. Retrieved from
https://medlineplus.gov/ency/article/002656.htm
3. Mayo Clinic. GERD and H2 Blockers. Retrieved from
https://www.mayoclinic.org/diseases-conditions/gerd/in-depth/gerd-medication/art-20046457
4. Cleveland Clinic. Antihistamines: Uses, Types and Side Effects. Retrieved from
https://my.clevelandclinic.org/health/treatments/antihistamines
5. U.S. National Library of Medicine. StatPearls – H2 Receptor Antagonists. Retrieved from
https://www.ncbi.nlm.nih.gov/books/NBK525994/
6. Goodman & Gilman’s: The Pharmacological Basis of Therapeutics (13th Edition).
7. Katzung, B. G., & Trevor, A. J. (2021). Basic and Clinical Pharmacology (15th ed.). McGraw Hill Education.
8. U.S. Food and Drug Administration (FDA). “FDA Requests Removal of All Ranitidine Products (Zantac) from the Market”. Retrieved from: https://www.fda.gov/news-events/press-announcements/fda-requests-removal-all-ranitidine-products-zantac-market
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