Question 1

Where are histamine H2 receptors located on parietal cells?

Accepted Answer

Histamine H2 receptors are G protein-coupled receptors located on the basolateral membrane of parietal cells. When histamine is released from enterochromaffin-like cells, it binds to these receptors and initiates the cyclic AMP pathway, which ultimately stimulates gastric acid secretion.

Question 2

How does the cyclic AMP pathway lead to gastric acid production?

Accepted Answer

When histamine binds to H2 receptors, adenylyl cyclase converts ATP to cAMP, increasing intracellular cAMP levels. This activates protein kinase A, which stimulates the proton pump to secrete hydrogen ions in exchange for potassium ions, producing gastric acid.

Question 3

What is the mechanism by which H2 receptor antagonists suppress gastric acid?

Accepted Answer

H2 receptor antagonists compete with histamine for H2 receptors, blocking histamine binding and suppressing gastric acid production. These blockers also reduce direct stimulation of parietal cells by acetylcholine or gastrin, further decreasing acid secretion through multiple pathways.

Question 4

What are the four main H2 receptor antagonists used clinically?

Accepted Answer

The four primary H2 receptor antagonists are cimetidine, ranitidine, famotidine, and nizatidine. These drugs effectively suppress gastric acid secretion during sleep, promoting ulcer healing and are administered as part of comprehensive treatment for peptic ulcer disease.

Question 5

How are H2 receptor antagonists metabolized and cleared from the body?

Accepted Answer

H2 receptor antagonists are metabolized in the liver and cleared through the kidneys. Due to this metabolic pathway, lower doses are advised for elderly patients or those with poor renal function to prevent drug accumulation and adverse effects.

Question 6

How do H2 antagonists compare to other acid suppressive approaches for peptic ulcer disease?

Accepted Answer

H2 receptor antagonists block histamine-mediated acid secretion, while acid suppressive drugs for peptic ulcer disease proton pump inhibitors directly inhibit the proton pump itself. Both approaches reduce gastric acid, but proton pump inhibitors provide more potent suppression by targeting the final step of acid secretion.

Question 7

Why is timing of H2 antagonist administration important for ulcer healing?

Accepted Answer

H2 receptor antagonists are most effective when administered during sleep because gastric acid secretion is naturally elevated at night. By suppressing acid during this period, these drugs allow the ulcer to heal without constant acid exposure, making nighttime dosing a key component of treatment strategy.

Acid Suppressive Drugs for Peptic Ulcer Disease: Histamine H2-Receptor Antagonists

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