Histamine H2 antagonists: Nursing pharmacology

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cimetidine (Tagamet HB), famotidine (Pepcid), nizatidine (Axid)
Histamine H2 receptor antagonists
Block H2 receptors in parietal cells of the stomach → decrease gastric acid secretion
  • Peptic ulcers
  • Gastroesophageal reflux disease (GERD)
  • Zollinger-Ellison syndrome
  • Prophylaxis of stress-induced ulcers
  • Cimetidine: PO, IV, IM
  • Famotidine: PO, IV
  • Nizatidine: PO
  • CNS: dizziness, somnolence, confusion, headache, hallucinations
  • Skin: pruritus, rash
  • Cardiovascular: hypotension, cardiac dysrhythmias
  • Gastrointestinal: diarrhea, constipation, decreased gastric acid
  • Pulmonary: aspiration pneumonia
  • Sexual: decreased libido, impotence
  • Prolonged use: vitamin B12 deficiency
  • Cimetidine: antiandrogenic effects (gynecomastia, galactorrhea)
  • Famotidine: seizures, QT prolongation, toxic epidermal necrolysis, Stevens-Johnson syndrome
  • Pregnancy and breastfeeding
  • Children < 16 years old
  • Elderly clients
  • Renal disease (dose adjustment)
  • Cimetidine and famotidine: hepatic disease
Assessment and monitoring: all Histamine H2 receptor antagonists
  • Baseline assessment
    • Vital signs, neurological status, gastrointestinal status, radiological or endoscopic results, hepatic function, ECG, vitamin B12

Client education: all Histamine H2 receptor antagonists
  • Reason and length of prescribed treatment
  • Timing of oral administration
  • Side effects
    • Cimetidine: gynecomastia and impotence
    • Famotidine: cardiac arrhythmias and decreased libido
  • Increase fluid intake and dietary Vitamin B12
  • Avoid alcohol, aspirin, NSAIDs, caffeine, spicy foods
  • Notify healthcare provider about adverse effects


Histamine H2-receptor antagonists, also called H2 blockers, are medications that help reduce the production of gastric acid.

Because of that, they can be used to treat peptic ulcers; gastroesophageal reflux disease, or GERD; and Zollinger-Ellison syndrome, which is a rare condition caused by gastrin-secreting tumors. In addition, histamine H2-receptor antagonists can be used to prevent stress-induced ulcers.

These medications include cimetidine, which can be administered orally, intravenously, and intramuscularly; famotidine, which is given orally or intravenously; and nizatidine, which is given orally.

Now, gastric acid is secreted by the parietal cells, which have different membrane receptors that modulate their activity. One of them is the H2 histamine receptor.

Normally, the stomach is protected from the acidic environment by the mucus secreted by foveolar cells, and the esophagus is protected by the lower esophageal sphincter, which prevents gastric acid from coming back up.

When some of these mechanisms fail, the person can develop peptic ulcers or gastroesophageal reflux disease.

Histamine H2-receptor antagonists block H2 receptors so histamine can’t bind them, which decreases gastric acid secretion, and in turn mitigates the harmful effects of gastric acid in these disorders.

Generally, histamine H2-receptor antagonists are safe medications. However, they may cause some side effects, since H2 receptors are not only located in the stomach.


  1. "Focus on Nursing Pharmacology" LWW (2019)
  2. "Pharmacology: A Patient-Centered Nursing Process Approach (8e)" Saunders (2014)
  3. "Mosby's 2021 Nursing Drug Reference" Mosby (2021)
  4. "Saunders Comprehensive Review for the NCLEX-RN Examination" Saunders (2020)

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