H2 Antagonists

Acid Controlling Agents

H2 antagonists (aka H2 receptor blockers): reduce but do not abolish stimulated acid secretion. They have become the most popular drugs for the treatment of many acid-related disorders including PUD. Available OTC in lower dosage forms. Cimedidine (Tagament), famotidine (pepcid), ranitidine (zantac), nizatidine. There is little difference among the 4 available drugs.

I Mechanism of action
A. Completely block histamine (H2) at the receptors of acid producing parietal cells
B. production of hydrogen ions is reduced, resulting in decreased production of HCl. This results in an increase in the pH of the stomach and relief of many of the symptoms associated with hyperacidity-related conditions.
II Drug Effect
A. Suppressed acid secretion in the stomach
III Indications: several therapeutic uses including treatment of:
A. GERD
B. PUD
C. erosive esophagitis
D. Adjunct therapy in control of upper GI bleeding
E. pathologic gastric hypersecretory conditions
IV Contraindications: known allergy
V Side effects:
A. overall, less than 3% incidence of side effects
B. Cimetidine may induce impotence and gynecomastia
C. May see: headaches, lethargy, confusion, diarrhea, urticaria, sweating, flushing, other
VI Interactions
A. Cimetidine carries a higher risk of drug interactions than the other three HA’s.
1. binds with P-450 microsomal oxidase system in the liver, resulting in inhibited oxidation of many drugs and increased drug levels.
B. All H2 antagonists may inhibit the absorption of drugs that require an acidic GI environment for absorption
C. Smoking has been shown to decrease the effectiveness of H2 blockers.
VII Nursing Implications
A. Assess for allergies and impaired renal of liver function.
B. Use with caution in patients who are confused, disoriented, or elderly
C. Take 1 hour before or after antacids
D. For intravenous doses, follow administration guidelines