Gastrointestinal Drugs and Medications Q 18

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Hydrochloric acid secretion is blocked by which of the following categories of drugs?

  

     A. Antacids

     B. Gastric stimulants

     C. Histamine-2 antagonists

     D. Antihistamines

    

    

Correct Answer: C. histamine-2 antagonists

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This is the only category of drugs that reduces the volume of secretions. H2RAs decrease gastric acid secretion by reversibly binding to histamine H2 receptors located on gastric parietal cells, thereby inhibiting the binding and action of the endogenous ligand histamine. H2 blockers thus function as competitive antagonists. By blocking the histamine receptor and thus histamine stimulation of parietal cell acid secretion, H2RAs suppress both stimulated and basal gastric acid secretion that is induced by histamine.

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Option A: The antacids reduce the acid reaching the duodenum by neutralizing the acid present in the stomach. The salts’ mechanism of neutralization of acid varies, and each salt has a different mechanism with the ultimate goal of acid neutralization. It is known to heal chronic ulcers and prevent acute mucosal damage induced chemically by reducing access to pepsin and acid.

Option B: Gastrointestinal stimulants are drugs that increase motility of the gastrointestinal smooth muscle, without acting as a purgative. These drugs have different mechanisms of action but they all work to move the contents of the gastrointestinal tract faster.

Option D: First-generation antihistamines easily cross the blood-brain barrier into the central nervous system and antagonize H-1 receptors, which leads to a different therapeutic and adverse effect profile in contrast to second-generation antihistamines, which selectively bind to peripheral histamine receptors.

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