Drugs Affecting Acid Secretion Quiz

See H2 Receptor Antagonists. Option B is correct because H2 receptor antagonists (H2RAs) such as famotidine competitively block histamine H2 receptors on the parietal cells of the stomach. Parietal cells secrete hydrochloric acid through the H+/K+ ATPase (the proton pump), and three signals converge on that pump: histamine, gastrin and acetylcholine. Histamine, released from enterochromaffin-like (ECL) cells in the stomach wall, binds H2 receptors on the parietal cell, raises cyclic AMP and switches the pump on. It is the dominant pathway for basal acid secretion, the background acid produced between meals, which is why blocking it is useful. H2RAs reduce acid secretion by around 60 to 70 percent and are particularly helpful for night-time symptoms, when the histamine drive predominates, but they block only one of the three pathways and so are weaker than proton pump inhibitors. Famotidine is the standard H2RA in current UK practice; ranitidine was withdrawn in 2019 after an MHRA recall because of nitrosamine contamination, and cimetidine is now rarely used because it inhibits liver enzymes and causes gynaecomastia. A memory aid: H2 blockers close one door of three, and PPIs close the final gate.

• Mechanism: H2 receptor antagonists such as famotidine competitively block histamine H2 receptors on parietal cells.
• Pathway: histamine is the dominant drive for basal acid secretion, alongside gastrin and acetylcholine.
• Strength: acid is reduced by around 60 to 70 percent, which is weaker than a proton pump inhibitor because only one of three pathways is blocked.