NCLEX Review Guide: Histamine (H2)-Receptor Antagonists

Mechanism of Action & Drug Classifications

• H2-receptor antagonists block histamine at H2 receptors in gastric parietal cells, reducing gastric acid secretion by up to 70%
• Common medications include ranitidine (Zantac), famotidine (Pepcid), cimetidine (Tagamet), and nizatidine (Axid)
• These drugs are less potent than proton pump inhibitors but provide rapid onset of action within 1-2 hours

Therapeutic Uses

• Primary indications include peptic ulcer disease, GERD, Zollinger-Ellison syndrome, and stress ulcer prophylaxis
• Used for short-term treatment of active ulcers (4-8 weeks) and long-term maintenance therapy
• Effective for preventing stress-related mucosal bleeding in critically ill patients

Administration Guidelines

1. Assess patient for abdominal pain, gastric bleeding, or signs of GI distress before administration
2. Administer oral doses with or without food, but avoid antacids within 1 hour as they may decrease absorption
3. Monitor for drug interactions, especially with cimetidine which inhibits cytochrome P450 enzymes
4. Evaluate therapeutic response by assessing symptom relief and healing of ulcers

Side Effects Profile

• Common side effects include headache, dizziness, constipation, and diarrhea occurring in less than 5% of patients
• Cimetidine may cause confusion, especially in elderly patients and can lead to gynecomastia with long-term use
• Rare but serious effects include blood dyscrasias, hepatotoxicity, and cardiac arrhythmias with IV administration

Teaching Points

• Instruct patients to take medication as prescribed, even if symptoms improve, to prevent ulcer recurrence
• Advise patients to avoid smoking and alcohol as these increase gastric acid production and delay healing
• Teach patients to report signs of GI bleeding including black tarry stools, coffee-ground emesis, or severe abdominal pain

High-Yield Testing Concepts

• Priority nursing action for patient on H2 antagonists with signs of GI bleeding is to assess vital signs and notify physician immediately
• When administering IV famotidine, dilute in 50-100mL of compatible solution and infuse over 15-30 minutes to prevent cardiac effects
• Patient teaching priority: complete full course of therapy even when asymptomatic to prevent ulcer recurrence