Generic and Brand Names
- cimetidine (Tagamet)
- ranitidine (formerly Zantac, withdrawn from the US market by the FDA in April 2020)
- famotidine (Pepcid, Zantac 360)
- nizatidine (Axid)
Therapeutic Action
H2 antagonists selectively block H2 receptors on the parietal cells. That prevents gastrin from triggering local histamine release, which blocks hydrochloric acid production, and it also cuts pepsin output from the chief cells.
Indications
Short-term treatment of active duodenal ulcer or benign gastric ulcer. Pathological hypersecretory conditions such as Zollinger-Ellison syndrome, by blocking the acid overproduction that drives them. Prophylaxis of stress-induced ulcers and acute upper GI bleeding in critical patients, since cutting acid protects a stomach lining already at risk from stress-reduced mucus. Erosive gastroesophageal reflux, where less regurgitated acid means healing and less pain. And relief of heartburn, acid indigestion, and sour stomach.
Pharmacokinetics
Cimetidine, ranitidine, and famotidine come in oral and parenteral forms.
Contraindications and Cautions
Do not use with a known allergy to any drug in the class. Use caution in pregnancy or lactation given potential fetal or neonatal effects, and in hepatic or renal dysfunction, which alters metabolism and excretion. Be careful with prolonged or continual use, since these drugs can mask a serious underlying condition.
Adverse Effects
CNS: dizziness, confusion, headache, somnolence. Cardiac: arrhythmias and cardiac arrest. GI: diarrhea. Reproductive: impotence. Skin: rash. Also gynecomastia.
Interactions
Cimetidine, famotidine, and ranitidine slow the metabolism of many drugs, raising serum levels and toxicity risk: warfarin and other anticoagulants, phenytoin, beta-adrenergic blockers, alcohol, quinidine, lidocaine, theophylline, chloroquine, benzodiazepines, nifedipine, pentoxifylline, TCAs, procainamide, and carbamazepine.
Nursing Considerations
Nursing Assessment
Screen for contraindications and cautions: allergy to any H2 antagonist, impaired renal or hepatic function, and current pregnancy or lactation. Take a detailed history of the GI problem (how long, prior medical evaluation) to confirm appropriate use and rule out an underlying condition. Get a baseline physical: inspect the skin for lesions or rash, evaluate neurological status (orientation and affect) for CNS effects, and assess cardiopulmonary status including pulse, blood pressure, and ECG if IV use is needed. Do an abdominal exam including the liver, and monitor liver and renal function tests for changes that might require a dose adjustment.
Nursing Diagnosis
- Acute pain related to CNS and GI effects
- Disturbed sensory perception (kinesthetic, auditory) related to CNS effects
- Decreased cardiac output related to cardiac arrhythmias
- Risk for injury related to CNS effects
- Deficient knowledge regarding drug therapy
Nursing Care Plans and Interventions
Give the drug with or before meals and at bedtime (exact timing varies by product) for therapeutic levels when acid is highest. Reduce the dose in hepatic or renal dysfunction to prevent toxicity. With IV doses, monitor continuously to catch serious adverse effects early, especially cardiac arrhythmias. Assess carefully for drug-drug interactions, since these agents act on liver enzyme systems. Provide comfort measures (analgesics, ready bathroom access, help with ambulation) to ease adverse effects. If CNS effects occur, reorient the patient periodically and institute safety measures to improve tolerance of the drug. Arrange regular followup to track drug effect and the underlying problem, offer support for coping with the regimen, and teach drug name, dosage, schedule, the need to space doses as ordered, ready bathroom access, and the adverse effects to watch for and how to minimize them.
Evaluation
Look for relief of GI symptoms, ulcer healing, and no progression of the ulcer. Watch for adverse effects (dizziness, confusion, hallucinations, GI changes, cardiac arrhythmias, hypotension, gynecomastia). Confirm the patient can name the drug, dosage, adverse effects, and the measures to avoid them, and monitor comfort measures and compliance.
Frequently Asked Questions
Is Zantac still available? Not as ranitidine. The FDA pulled all ranitidine products, including Zantac, from the US market on April 1, 2020 because the drug can contain NDMA, a probable carcinogen, at levels that rise over time (FDA). The product sold as Zantac 360 today contains famotidine, a different H2 antagonist.
Why is cimetidine the one to watch for interactions? Cimetidine is a potent inhibitor of the cytochrome P450 enzymes (CYP1A2, CYP2C9, CYP2D6), so it slows the breakdown of many drugs and raises their levels, including warfarin, phenytoin, theophylline, and others. Famotidine and nizatidine carry far less interaction risk (H2 Blockers, StatPearls).
How do H2 antagonists actually lower acid? They block the H2 receptor on the parietal cell, so histamine can no longer trigger hydrochloric acid release, and pepsin output drops as well. Less acid means ulcers and reflux can heal.
When should the dose be reduced? In hepatic or renal dysfunction, since the liver and kidneys clear these drugs and impaired clearance raises blood levels and toxicity risk. Confirm liver and renal function before and during therapy.
What CNS effects should you watch for, and in whom? Dizziness, confusion, headache, and somnolence, most often in older adults and in patients with reduced renal or hepatic function. Reorient the patient and put fall precautions in place if these appear.
Why does prolonged use need a second look? These drugs can relieve symptoms well enough to mask a more serious underlying problem, such as gastric cancer. Persistent or recurring symptoms warrant evaluation rather than indefinite self-treatment.