Histamine-2 Antagonists
Histamine-2 (H2) receptor antagonists block the release of acid in response to gastrin or parasympathetic release.
Histamine-2 Antagonist: Generic and Brand Names
Here is a table of the most commonly used H2 antagonists.
| Classification | Generic name | Brand name |
| Histamine-2 antagonists | cimetidine | Tagamet |
| ranitidine | Zantac | |
| famotidine | Pepcid | |
| nizatidine | Axid |
Description
Histamine-2 antagonists block the release of hydrochloric acid in response to gastrin.
- These drugs include cimetidine (Tagamet), ranitidine (Zantac), famotidine (Pepcid), and nizatidine (Axid).
Therapeutic actions
The desired actions of H2 antagonists include the following:
- Selectively block H2 receptors located on the parietal cells.
- Prevents the release of gastrin, a hormone that causes local release of histamine (due to stimulation of histamine receptors), ultimately blocking the production of hydrochloric acid.
- Decreases pepsin production by the chief cells.
Indication
Histamine-2 antagonists are indicated for the following:
- Short-term treatment of active duodenal ulcer or benign gastric ulcer.
- Treatment of pathological hypersecretory conditions such as Zollinger-Ellison syndrome (blocking the overproduction of hydrochloric acid that is associated with these conditions).
- Prophylaxis of stress-induced ulcers and acute upper GI bleeding in critical patients (blocking the production of acid protects the stomach lining, which is at risk because of decreased mucus production associated with extreme stress).
- Treatment of erosive gastroesophageal reflux (decreasing the acid being regurgitated into the esophagus will promote healing and decrease pain).
- Relief of symptoms of heartburn, acid indigestion, and sour stomach.
Pharmacokinetics
Cimetidine, ranitidine, and famotidine are available in oral and parenteral forms
| Route | Onset | Peak | Duration |
| Oral | Varies | 1-1.5 h | 4-5 h |
| IM, IV | Rapid | 1-1.5 h | 4-5 h |
| T 1/2: 2 hours | |||
| Metabolization: Liver | |||
| Excretion: Urine |
Contraindications and Cautions
The contraindications and cautions when using H2 antagonists include:
- Allergy. The H2 antagonists should not be used with known allergy to any drugs of this class to prevent hypersensitivity reactions.
- Pregnancy or lactation. Caution should be used during pregnancy or lactation because of the potential for adverse effects on the fetus or nursing baby.
- Hepatic or renal dysfunction. Caution should be used in patients with hepatic or renal dysfunction, which could interfere with drug metabolism and excretion.
- Prolonged or continual use. Care should also be taken if prolonged or continual use of these drugs is necessary because they may be masking serious underlying conditions.
Adverse effects
The adverse effects associated with H2 antagonists are:
- CNS: Dizziness, confusion, headache, somnolence.
- Cardio: Cardiac arrhythmias, cardiac arrest.
- GI: Diarrhea.
- Reproductive: Impotence.
- Skin: Rash.
- Misc: Gynecomastia.
Interactions
Cimetidine, famotidine, and ranitidine can slow down the metabolism of the following drugs, leading to increased serum levels and possible toxic reactions:
- Warfarin.
- Anti-coagulants.
- Phenytoin.
- Beta-adrenergic blockers.
- Alcohol.
- Quinidine.
- Lidocaine.
- Theophylline.
- Chloroquine.
- Benzodiazepines.
- Nifedipine.
- Pentoxifylline.
- TCAs.
- Procainamide.
- Carbamazepine.
Nursing Considerations
Nursing considerations for a patient using H2 antagonists include the following:
Nursing Assessment
Nursing assessment for a patient using H2 antagonists include:
- Assess for possible contraindications and cautions: history of allergy to any H2 antagonists to prevent potential allergic reactions; impaired renal or hepatic function, which could affect the metabolism and excretion of the drug; a detailed description of the GI problem, including length of time of the disorder and medical evaluation to evaluate the appropriate use of the drug and possibility of underlying medical problems; and current status of pregnancy and lactation because of the potential for adverse effects on the fetus or newborn.
- Perform a physical examination to establish baseline data before beginning therapy, determine effectiveness of the therapy, and evaluate for any adverse effects associated with drug therapy.
- Inspect the skin for evidence of lesions or rash to monitor for adverse reactions.
- Evaluate neurological status, including orientation and affect, to assess CNS effects of the drug and to plan for protective measures.
- Assess cardiopulmonary status, including pulse, blood pressure, and electrocardiogram (if IV use is needed), to evaluate the cardiac effects of the drug.
- Perform abdominal examination, including assessment of the liver, to establish a baseline and rule out underlying medical problem.
- Monitor the results of laboratory tests, including liver and renal function tests, to predict changes in metabolism or excretion of the drug that might require dose adjustment.
- 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 interventions for patients using H2 antagonists include:
- Ensure therapeutic levels. Administer drug with or before meals and at bedtime (exact timing varies with product) to ensure therapeutic levels when the drug is most needed.
- Prevent serious toxicity. Arrange for decreased dose in cases of hepatic or renal dysfunction to prevent serious toxicity.
- Monitor IV doses carefully. Monitor the patient continually if giving IV doses to allow early detection of potentially serious adverse effects, including cardiac arrhythmias
- Assess for potential drug-drug interactions. Assess the patient carefully for any potential drug-drug interactions if given in combination with other drugs because of the drugs effects on liver enzyme systems.
- Provide patient’s comfort. Provide comfort, including analgesics, ready to access bathroom facilities, and assistance with ambulation, to minimize possible adverse effects.
- Reorient patient thoroughly. Periodically reorient the patient and institute safety measures if CNS effects occur to ensure patient safety and improve and improve patient tolerance of the drug and drug effects.
- Attend regular follow-ups. Arrange for regular follow-up to evaluate drug effects and the underlying problems.
- Provide support. Offer support and encouragement to help patients cope with the disease and the drug regimen.
- Educate the client. Provide patient teaching regarding drug name, dosage, and schedule for administration; importance of spacing administration appropriately as ordered; need for readily available access to bathroom; signs and symptoms of adverse effects and measures to minimize or prevent them.
Evaluation of a patient using H2 antagonists include:
- Monitor patient response to the drug (relief of GI symptoms, ulcer healing, prevention of progression of ulcer).
- Monitor for adverse effects (dizziness, confusion, hallucinations, GI alterations, cardiac arrhythmias, hypotension, gynecomastia).
- Evaluate the effectiveness of the teaching plan (patient can name drug, dosage, adverse effects to watch for, and specific measures to avoid them).
- Monitor the effectiveness of comfort measures and compliance with the regimen.
1. Which of the following best describes the method of action of medications, such as ranitidine (Zantac), which are used in the treatment of peptic ulcer disease?
A. Neutralize acid
B. Reduce acid secretions
C. Stimulate gastrin release
D. Protect the mucosal barrier
1. Answer: B. Reduce acid secretions.
- Option B: Ranitidine is a histamine-2 receptor antagonist that reduces acid secretion by inhibiting gastrin secretion.
2. A client is to take one daily dose of ranitidine (Zantac) at home to treat her peptic ulcer. The nurse knows that the client understands proper drug administration of ranitidine when she says that she will take the drug at which of the following times?
A. Before meals
B. With meals
C. At bedtime
D. When pain occurs
2. Answer: C. At bedtime.
- Option C: Ranitidine blocks secretion of hydrochloric acid. Clients who take only one daily dose of ranitidine are usually advised to take it at bedtime to inhibit nocturnal secretion of acid.
3. The nurse provides medication instructions to a client with peptic ulcer disease. Which statement, if made by the client, indicates the best understanding of the medication therapy?
A. “The cimetidine (Tagamet) will cause me to produce less stomach acid.”
B. “Sucralfate (Carafate) will change the fluid in my stomach.”
C. “Antacids will coat my stomach.”
D. “Omeprazole (Prilosec) will coat the ulcer and help it heal.”
3. Answer: A. “The cimetidine (Tagamet) will cause me to produce less stomach acid.”
- Option A: Cimetidine (Tagamet), a histamine H2 receptor antagonist, will decrease the secretion of gastric acid.
- Option B: Sucralfate (Carafate) promotes healing by coating the ulcer.
- Option C: Antacids neutralize acid in the stomach.
- Option D: Omeprazole (Prilosec) inhibits gastric acid secretion.
4. When a client has peptic ulcer disease, the nurse would expect a priority intervention to be:
A. Assisting in inserting a Miller-Abbott tube
B. Assisting in inserting an arterial pressure line
C. Inserting a nasogastric tube
D. Inserting an I.V.
4. Answer: C. Inserting a nasogastric tube.
- Option C: An NG tube insertion is the most appropriate intervention because it will determine the presence of active GI bleeding.
- Option A: A Miller-Abbott tube is a weighted, mercury-filled ballooned tube used to resolve bowel obstructions.
- Options B and D: There is no evidence of shock or fluid overload in the client; therefore, an arterial line is not appropriate at this time and an IV is optional.
5. A 40-year-old male client has been hospitalized with peptic ulcer disease. He is being treated with a histamine receptor antagonist (cimetidine), antacids, and diet. The nurse doing discharge planning will teach him that the action of cimetidine is to:
A. Reduce gastric acid output.
B. Protect the ulcer surface.
C. Inhibit the production of hydrochloric acid (HCl).
D. Inhibit vagus nerve stimulation.
5. Answer: A. Reduce gastric acid output.
- Option A: These drugs inhibit the action of histamine on the H2 receptors of parietal cells, thus reducing gastric acid output.