H2 antagonists are medications that reduce stomach acid production by blocking histamine-2 receptors in the stomach cells. They are commonly used to treat various gastrointestinal conditions and prevent stress ulcers.
Generic names: Famotidine, Ranitidine (discontinued), Cimetidine, Nizatidine
Brand names: Pepcid, Tagamet, Axid, Zantac (discontinued)
Pharmacologic class: Histamine-2 receptor antagonist
Therapeutic class: Antiulcer agent, Gastric acid secretion inhibitor
Mechanism of action: H2 antagonists work by competitively blocking histamine-2 receptors in the gastric parietal cells, reducing gastric acid secretion and increasing gastric pH.
Indications for use: Treatment of gastroesophageal reflux disease (GERD), peptic ulcer disease, Zollinger-Ellison syndrome, prevention of stress ulcers in critically ill patients, and management of heartburn symptoms.
Precautions and contraindications: Known hypersensitivity to H2 antagonists, severe renal impairment, pregnancy (Category B), breastfeeding mothers, elderly patients, and those with liver dysfunction.
Drug Interactions
- Antacids may decrease the absorption of H2 antagonists
- May increase levels of certain medications including theophylline, warfarin, and phenytoin
- Can reduce the absorption of iron salts and certain antibiotics
- It may interfere with the absorption of azole antifungals
Adverse Effects
- Headache and dizziness
- Confusion and agitation (especially in the elderly)
- Diarrhea or constipation
- Muscle pain or weakness
- Irregular heartbeat
- Skin rash or itching
- Changes in liver function tests
- Gynecomastia (particularly with cimetidine)
Administration Considerations
Available preparations: Oral tablets (regular and chewable), oral suspension, and injectable forms
Dosages: Vary by drug and indication. For famotidine:
- GERD: 20 mg PO twice daily
- Ulcer treatment: 40 mg PO daily at bedtime
- Stress ulcer prophylaxis: 20 mg IV every 12 hours
Routes of administration include:
- Oral: Onset 1 hour, peak 1-3 hours, duration 6-12 hours
- IV: Onset 15-30 minutes, peak 30-60 minutes, duration 6-12 hours
Nursing Considerations for H2 Antagonists
Related Nursing Diagnoses
- Risk for impaired gastric mucosal integrity
- Acute pain related to gastric hyperacidity
- Risk for fluid volume deficit
- Deficient knowledge related to medication regimen
- Risk for bleeding related to stress ulcers
Nursing Assessment
- Assess the patient’s gastrointestinal symptoms and history.
- Monitor for signs of GI bleeding
- Assess renal function through BUN and creatinine levels
- Evaluate mental status, especially in elderly patients
- Check for drug allergies and current medication list
Nursing Interventions
- Administer oral doses with meals for optimal absorption
- Monitor for signs of bleeding in high-risk patients
- Assess mental status changes, particularly in the elderly
- Monitor renal function in patients with kidney disease
- For IV administration, follow specific dilution guidelines
Patient Teaching Associated with H2 Antagonists
- Take medication as prescribed at the same time each day
- Report signs of GI bleeding: black stools, coffee-ground vomitus
- Avoid alcohol and smoking while taking medication
- Space antacids at least 1 hour apart from H2 antagonists
- Maintain an upright position for 30 minutes after taking the medication
- Report persistent side effects to a healthcare provider
- Continue medication as prescribed even if symptoms improve
This is not an all-inclusive list of possible drug interactions, adverse effects, precautions, nursing considerations, or patient instructions. Please consult further with a pharmacist for complete information.
References and Sources
- Kistenfeger, Q., Haight, P., Wang, H., Levine, M., Chalif, J., Backes, F., O’Malley, D., & Chambers, L. (2024). The effect of antibiotics, proton pump inhibitors, H2-receptor antagonists, and steroids on survival among ovarian cancer patients receiving PARP inhibitor therapy. Gynecologic Oncology, 190, S312. https://doi.org/10.1016/j.ygyno.2024.07.469
- Li J, Wang F, Lv L, Xu L, Zeng E, Tang X. Histamine H2 antagonists for functional dyspepsia: A protocol for a systematic review and meta-analysis. Medicine (Baltimore). 2019 Nov;98(47):e18128. doi: 10.1097/MD.0000000000018128. PMID: 31764854; PMCID: PMC6882590.
- Savarino V, Mela GS, Scalabrini P, Celle G. H2-receptor antagonist non-responders. Lancet. 1987 Nov 28;2(8570):1281. doi: 10.1016/s0140-6736(87)91898-8. PMID: 2890898.
- Silvestri, L. A. (2020). Saunders comprehensive review for the NCLEX-RN examination. St. Louis, MO: Elsevier.
- Zhang J, Cai WK, Zhang Z, Wang P, Lin XQ, Feng J, Fu SC, He GH. Cardioprotective effect of histamine H2 antagonists in congestive heart failure: A systematic review and meta-analysis. Medicine (Baltimore). 2018 Apr;97(15):e0409. doi: 10.1097/MD.0000000000010409. PMID: 29642208; PMCID: PMC5908598.
