A 42-year-old woman comes to the office due to a 2-month history of an intermittent burning sensation in her chest with an occasional simultaneous acidic taste at the back of her throat. The symptoms occur soon after she eats a meal. The patient has no shortness of breath, lightheadedness, nausea, vomiting, or weight loss. She has no other medical conditions. The patient has smoked a pack of cigarettes daily for the last 10 years but does not use alcohol. Family history is unremarkable. Vital signs are within normal limits. BMI is 32 kg/m². Physical examination shows no abnormalities. Urine pregnancy test is negative. Smoking cessation is discussed, and a medication is prescribed for treatment of her symptoms. The patient returns in 2 weeks for a follow-up visit and reports near-complete resolution of her symptoms. Which of the following is the most likely mechanism of action of this drug?

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Quizplus · Accepted Answer

11ec160b_3bd0_4905_9249_8106c0547c4a_MD0001_00 This patient's heartburn is likely related to gastroesophageal reflux disease (GERD), a common disorder that occurs when gastric acid refluxes into the esophagus. Management consists of lifestyle and dietary modifications (eg, weight loss, avoidance of tobacco) as well as medications that suppress gastric acid secretion. Proton pump inhibitors (PPIs) (eg, pantoprazole, omeprazole) are the most effective inhibitors of gastric acid secretion. They bind to and irreversibly inhibit the H⁺/K⁺ ATPase on parietal cells. Side effects are related to elevated gastric pH and include an increased risk of Clostridioides difficile and nutritional deficiencies (eg, calcium, magnesium, iron). Although less potent than PPIs, histamine 2 receptor antagonists (eg, famotidine, cimetidine) are also used as first-line therapy for GERD. They inhibit gastric acid secretion by targeting histamine receptors on parietal cells. These medications are less side effect-prone than PPIs; however, they have a slower onset of action, and tachyphylaxis is common. (Choice A) Gastrin, a hormone released from G cells, binds to cholecystokinin (CCK) B receptors and stimulates gastric acid secretion both directly (through binding on parietal cells) and indirectly (through binding on enterochromaffin-like cells to increase histamine release). CCK receptor antagonists are not routinely used in clinical practice. (Choice B) Sucralfate forms a viscous paste in the stomach, providing a cytoprotective layer that prevents the diffusion of gastric acid. It is less effective than PPIs and is typically used as an adjunctive medication for peptic ulcer disease. (Choice D) Octreotide is a somatostatin analogue that inhibits gastrin synthesis (as well as many other gastrointestinal hormones). It is sometimes used in Zollinger-Ellison syndrome, but is not routinely used for GERD. (Choice E) Misoprostol is a prostaglandin E1 analogue that binds prostaglandin receptors on parietal cells, reducing gastric acid production and inducing secretion of mucus and bicarbonate. Misoprostol can be used to prevent NSAID-induced gastric ulcers, but is less helpful for treating GERD; its significant uterotonic effects (eg, uterine contractions, cervical ripening) also limit its use in women of childbearing age. Educational objective: Management of gastroesophageal reflux disease includes lifestyle and dietary modifications (eg, weight loss, tobacco avoidance) and medications such as proton pump inhibitors (PPIs) (eg, pantoprazole, omeprazole) or histamine 2 receptor antagonists (eg, ranitidine). PPIs irreversibly inhibit the H⁺/K⁺ ATPase on parietal cells, which decreases gastric acid secretion.

A 42-Year-Old Woman Comes to the Office Due to a 2-Month