A patient is receiving histamine receptor antagonist for peptic ulcers and ask to the nurse about mode of action of histamine receptor antagonist. The best response given by the nursing officer is?

1. A

   Decreases activity of acetylcholine

2. B

   Decreases gastric acid secretions

3. C

   Pain reduction

4. D

   Increases peristalsis

Appeared in: PGIMER NO - 2020

Explanation

• Histamine-2 (H2) receptor antagonists work by selectively and competitively blocking H2 receptors on the parietal cells of the stomach.
• This blockage prevents histamine from binding to the receptors and stimulating the H+/K+ ATPase proton pump, the final step in acid production.
• The primary result is a significant reduction in both basal (night-time) and meal-stimulated gastric acid secretion, which allows peptic ulcers to heal.

Why Other Options Were Wrong

• Option A: This describes the action of anticholinergic drugs, which block muscarinic receptors for acetylcholine, not H2 receptors for histamine.
• Option C: Pain reduction is a desired therapeutic outcome resulting from decreased acid irritation, not the drug's direct pharmacological mechanism of action.
• Option D: This is the mechanism of prokinetic agents, such as metoclopramide, which enhance gastrointestinal motility. H2 blockers do not have a direct effect on peristalsis.

Related Visual

Clinical Relevance

• Nursing practice connection: Use the key finding related to Mechanism of Action of H2 Receptor Antagonists to guide bedside assessment, documentation, and the next nursing action.
• Educating patients on the mechanism of action helps improve adherence and understanding of why lifestyle changes (e.g., avoiding smoking, alcohol, NSAIDs) are also crucial for ulcer healing.
• Nurses must monitor for central nervous system (CNS) side effects like confusion and dizziness, particularly in elderly patients or those with renal impairment, as the drugs are cleared by the kidneys.
• What if? If the patient were taking a Proton Pump Inhibitor (PPI) like Omeprazole, the mechanism would be different and more potent. PPIs irreversibly block the H+/K+ ATPase (proton pump) itself, the final common pathway for acid secretion, leading to a more profound and longer-lasting reduction in acid.

How to Approach the Question

• First, identify the core of the question: it asks for the 'mode of action' of a 'histamine receptor antagonist'.
• Recall the physiology of gastric acid secretion. Remember that histamine is a key stimulant for acid release from parietal cells.
• Understand that an 'antagonist' is a blocker. Therefore, a histamine antagonist must block histamine's effect.
• Evaluate the options. 'Decreases gastric acid secretions' directly describes the result of blocking histamine's stimulating effect on the stomach's parietal cells.
• Differentiate the 'mechanism of action' (how the drug works at a cellular level) from the 'therapeutic effect' (the clinical result, like pain reduction).
• Eliminate options describing the mechanisms of other drug classes, such as anticholinergics (affecting acetylcholine) or prokinetics (affecting peristalsis).

Concept Tested & Keywords

• Concept Tested: Mechanism of Action of H2 Receptor Antagonists
• Stem keywords: histamine receptor antagonist, peptic ulcers, mode of action
• Lead-in keywords: best response

Question ID

QO-8OGMWn5fMmmRgFF68z9

Copy ID

Reference Book

E6 Pharmacology KD Tripathi Essentials 9e Part 2 p. 323-325

E6 Pharmacology Katzung 16e p. 1695-1697