A 67-year-old man presents to his physician accompanied by his wife. She states that recently her husband has been confused and has suffered multiple falls in the past few days. The patient has a history of hypertension, hyperlipidemia, and gastroesophageal reflux disease. He was prescribed a medication for heartburn symptoms several months ago.
Based on the presenting symptoms, which of the following is the mechanism of action of the medication most likely prescribed to this patient?
E) Reversible inhibition of H2 receptors in stomach parietal cells
Based on the patient's side effects of dizziness and confusion, it is most likely that he was prescribed an H2 blocker to treat his symptoms of heartburn. H2 blockers reversibly block H2 receptors on stomach parietal cells, leading to decreased acid production. Common side effects of H2 blockers include anti-androgenic effects (erectile dysfunction, gynecomastia, decreased libido) but also can cross the blood-brain barrier causing confusion, dizziness, and headaches.
Answer choice A: Antagonism at 5-HT3 receptors, is incorrect. This is the mechanism of ondansetron, which is used as an anti-emetic and is not a treatment for heartburn. Common side effects of this drug include headache, constipation, long QT syndrome, and serotonin syndrome.
Answer choice B: Increased production and secretion of gastric mucous barrier, is incorrect. This is the mechanism of action of prostaglandin analogs, most commonly misoprostol. These drugs are usually well-tolerated, but a common side effect of these drugs is diarrhea.
Answer choice C: Irreversible inhibition of H+/K+ ATPase in stomach parietal cells, is incorrect. This is the mechanism of action of proton pump inhibitors (PPI). Common side effects of these drugs include pneumonia, hypomagnesemia, and increased risk of Clostridium difficile infections.
Answer choice D: Neutralization of stomach pH, is incorrect. This is the mechanism of action of antacids. Different formulations of antacids exist, but all can cause hypokalemia. Side effects of aluminum hydroxide include constipation and hypophosphatemia. Side effects of calcium carbonate include hypercalcemia. Side effects of magnesium hydroxide include diarrhea, hyporeflexia, hypotension, and cardiac arrest.
Key Learning Point
H2 blockers work through reversible inhibition of H2 receptors in stomach parietal cells. Common side effects of H2 blockers include anti-androgenic effects (erectile dysfunction, gynecomastia, decreased libido), but they also can cross the blood-brain barrier causing confusion, dizziness, and headaches.
