1. Metoclopramide and domperidone are both dopamine D2 receptor antagonists used as prokinetics, yet their adverse-effect profiles differ sharply. Which statement most precisely distinguishes the two?
A) Metoclopramide prolongs the QTc interval through hERG channel blockade, whereas domperidone causes extrapyramidal symptoms through central D2 blockade
B) Both agents cross the blood-brain barrier freely and carry identical extrapyramidal risk
C) Metoclopramide crosses the blood-brain barrier and therefore carries extrapyramidal and tardive dyskinesia risk, whereas domperidone is largely excluded from the CNS (a P-glycoprotein substrate) and instead carries QTc prolongation risk
D) Neither agent crosses the blood-brain barrier, so both are free of central adverse effects
E) Domperidone crosses the blood-brain barrier more readily than metoclopramide, giving it greater extrapyramidal risk
ANSWER: C
Rationale:
The discriminator between these two D2 antagonists is blood-brain barrier (BBB) penetration. Metoclopramide crosses the BBB freely, producing central D2 blockade and therefore extrapyramidal symptoms, tardive dyskinesia, and hyperprolactinemia. Domperidone is a P-glycoprotein (P-gp, an efflux transporter) substrate and is largely excluded from the CNS, so it spares patients the extrapyramidal effects but instead carries the principal risk of QTc prolongation via cardiac hERG channel blockade.
Option A: Option A inverts the two profiles.
Option B: Option B is incorrect because domperidone does not cross the BBB freely and the two do not share identical extrapyramidal risk.
Option D: Option D is incorrect because metoclopramide does cross the BBB.
Option E: Option E reverses the relationship: metoclopramide, not domperidone, is the agent that readily enters the CNS.
2. A clinician must choose between ondansetron and palonosetron for a patient with borderline QTc prolongation who also needs coverage for delayed nausea. Which statement correctly discriminates the two 5-HT3 receptor antagonists?
A) Palonosetron has a substantially longer half-life and minimal hERG channel affinity, so it both covers the delayed phase better and carries little clinically significant QTc risk, whereas ondansetron has a shorter half-life and causes dose-dependent QTc prolongation
B) Ondansetron has the longer half-life and is preferred for delayed-phase coverage, whereas palonosetron is short-acting
C) Both agents have identical half-lives and identical hERG affinity, so the choice is arbitrary
D) Palonosetron carries the greater QTc risk because of its high hERG affinity, whereas ondansetron is hERG-sparing
E) Ondansetron is a second-generation agent with no QTc effect, whereas palonosetron is a first-generation agent with marked QTc risk
ANSWER: A
Rationale:
Palonosetron is distinguished from ondansetron by a substantially longer half-life (approximately 40 hours) and higher receptor binding affinity, giving it superior delayed-CINV coverage, together with minimal hERG (human ether-a-go-go-related gene) channel affinity, so it does not cause clinically significant QTc prolongation at therapeutic doses. Ondansetron, by contrast, is shorter-acting and causes dose-dependent QTc prolongation, which is why the FDA advises against single IV doses greater than 32 mg.
Option B: Option B reverses the half-life relationship.
Option C: Option C is incorrect because the two differ markedly in both half-life and hERG affinity.
Option D: Option D inverts the hERG profiles.
Option E: Option E is incorrect because it misassigns the generations and inverts the QTc risk: palonosetron is the newer, hERG-sparing agent.
3. Aprepitant and rolapitant are both NK1 receptor antagonists used for delayed chemotherapy-induced nausea and vomiting. Which property most clearly distinguishes rolapitant from aprepitant?
A) Rolapitant is a 5-HT3 antagonist, whereas aprepitant is an NK1 antagonist
B) Rolapitant must be given intravenously, whereas aprepitant is oral only
C) Rolapitant has a markedly shorter half-life than aprepitant, requiring multiple daily doses
D) Rolapitant is a strong CYP3A4 inducer, whereas aprepitant is a CYP3A4 inhibitor
E) Rolapitant does not inhibit CYP3A4, giving it a simpler drug-interaction profile, whereas aprepitant is a moderate CYP3A4 inhibitor that raises concentrations of co-administered CYP3A4 substrates such as dexamethasone
ANSWER: E
Rationale:
The key distinction is the drug-interaction profile. Rolapitant does not inhibit CYP3A4, which simplifies its interaction profile, whereas aprepitant is both a CYP3A4 substrate and a moderate CYP3A4 inhibitor that raises plasma concentrations of co-administered CYP3A4 substrates such as dexamethasone (prompting a dexamethasone dose reduction).
Option A: Option A is incorrect: both rolapitant and aprepitant are NK1 antagonists, not 5-HT3 antagonists.
Option B: Option B is incorrect: rolapitant is available orally, and the relevant distinction is metabolic, not route-based.
Option C: Option C inverts the half-life relationship: rolapitant has a very long half-life (exceeding 160 hours), allowing single-dose coverage.
Option D: Option D is incorrect: aprepitant inhibits (it does not strongly induce) CYP3A4, and rolapitant is not characterized by strong CYP3A4 induction.
4. The acute and delayed phases of chemotherapy-induced nausea and vomiting are driven by different mediators and receptors. Which pairing correctly matches each phase to its principal mediator?
A) Acute phase: substance P at NK1 receptors; delayed phase: serotonin at 5-HT3 receptors
B) Acute phase (within 24 hours): serotonin from enterochromaffin cells acting at 5-HT3 receptors; delayed phase (days 2 to 5): substance P acting at NK1 receptors
C) Acute phase: dopamine at D2 receptors; delayed phase: histamine at H1 receptors
D) Acute phase: acetylcholine at muscarinic receptors; delayed phase: serotonin at 5-HT4 receptors
E) Both phases are mediated solely by serotonin at 5-HT3 receptors, differing only in intensity
ANSWER: B
Rationale:
The acute phase of CINV (chemotherapy-induced nausea and vomiting), within the first 24 hours, is driven primarily by serotonin released from enterochromaffin (EC) cells acting on 5-HT3 receptors on vagal afferents, which is why 5-HT3 antagonists are the cornerstone of acute prophylaxis. The delayed phase (peaking at 48 to 72 hours and persisting through day 5) is mediated by substance P acting at NK1 receptors, which is the target of NK1 antagonists such as aprepitant.
Option A: Option A reverses the two pairings.
Option C: Option C is incorrect because it misassigns dopamine and histamine to these phases.
Option D: Option D is incorrect because it misassigns acetylcholine and 5-HT4.
Option E: Option E is incorrect because the two phases are mediated by distinct transmitter-receptor systems, not by 5-HT3 alone.
5. Metoclopramide is sometimes described as having a broader receptor profile than a simple dopamine antagonist. Which description most precisely captures its mechanism?
A) A pure dopamine D2 receptor antagonist with no other receptor activity
B) A selective 5-HT4 receptor agonist with no dopaminergic activity
C) A motilin receptor agonist that also blocks histamine H1 receptors
D) A substituted benzamide that blocks dopamine D2 receptors in the gut and CNS, and at higher doses also blocks 5-HT3 receptors and partially activates 5-HT4 receptors
E) A muscarinic M1 antagonist that secondarily blocks dopamine D2 receptors
ANSWER: D
Rationale:
Metoclopramide is a substituted benzamide that blocks dopamine D2 receptors in both the gut wall and the CNS, and at higher doses additionally blocks 5-HT3 receptors and partially activates 5-HT4 receptors. This combined profile underlies both its prokinetic effect (D2 blockade disinhibiting enteric acetylcholine release, plus 5-HT4 agonism) and its antiemetic effect (central D2 blockade at the chemoreceptor trigger zone).
Option A: Option A understates the profile by calling it a pure D2 antagonist.
Option B: Option B is incorrect: metoclopramide has prominent dopaminergic blocking activity, not selective 5-HT4 agonism.
Option C: Option C describes erythromycin-like motilin agonism, which metoclopramide does not possess.
Option E: Option E is incorrect because it misassigns a muscarinic mechanism that is not the basis of metoclopramide's action.
6. Erythromycin and metoclopramide are both prokinetics, but the limitation that constrains long-term use differs between them. Which statement correctly identifies the principal limiting factor for each?
A) Both are limited primarily by tardive dyskinesia risk with prolonged use
B) Both are limited primarily by tachyphylaxis from receptor downregulation
C) Metoclopramide is limited by tardive dyskinesia risk (a black-box 12-week limit), whereas erythromycin is limited by tachyphylaxis from motilin receptor downregulation within days to weeks
D) Metoclopramide is limited by tachyphylaxis, whereas erythromycin is limited by tardive dyskinesia
E) Erythromycin is limited by extrapyramidal symptoms, whereas metoclopramide is limited by antibiotic resistance
ANSWER: C
Rationale:
The two prokinetics are constrained by entirely different mechanisms. Metoclopramide is limited by the risk of tardive dyskinesia from prolonged central D2 blockade, the basis for its FDA black-box 12-week limit. Erythromycin, a motilin receptor agonist, is limited by tachyphylaxis: motilin receptor downregulation develops within days to weeks of continuous use, reducing prokinetic efficacy, so it is best reserved for acute exacerbations.
Option A: Option A is incorrect because erythromycin's limitation is tachyphylaxis, not tardive dyskinesia.
Option B: Option B is incorrect because metoclopramide's limitation is tardive dyskinesia, not tachyphylaxis.
Option D: Option D reverses the two limitations.
Option E: Option E misattributes extrapyramidal symptoms to erythromycin and an antibiotic-resistance concern to metoclopramide, neither of which is correct.
7. Prochlorperazine and promethazine are both phenothiazines used as antiemetics. Which statement correctly distinguishes promethazine from prochlorperazine?
A) Promethazine has substantial histamine H1 antihistamine and anticholinergic activity contributing to its antiemetic effect and carries an FDA black box warning for fatal respiratory depression in children under age 2
B) Promethazine is devoid of antihistamine activity and acts purely through dopamine D2 blockade
C) Promethazine carries no pediatric warning, whereas prochlorperazine is contraindicated in all children
D) Promethazine is a butyrophenone, whereas prochlorperazine is a phenothiazine
E) Promethazine is a selective NK1 antagonist used for delayed CINV
ANSWER: A
Rationale:
Promethazine, although a phenothiazine, is distinguished by significant histamine H1 antihistamine and anticholinergic activity that contributes to its antiemetic effect through vestibular and CNS pathways, making it useful for motion sickness and postoperative nausea. It also carries an FDA black box warning for fatal respiratory depression in children under age 2.
Option B: Option B is incorrect because promethazine has prominent antihistamine activity rather than acting purely via D2 blockade.
Option C: Option C is incorrect: the pediatric black box warning applies to promethazine.
Option D: Option D is incorrect: both drugs are phenothiazines, not butyrophenones.
Option E: Option E is incorrect because promethazine is not an NK1 antagonist and is not used for delayed CINV.
8. Scopolamine is the most effective single agent for motion sickness. Which statement most precisely describes its mechanism and the basis for its efficacy in vestibular nausea?
A) It is a serotonin 5-HT3 antagonist that blocks vagal afferent signaling from the gut
B) It is a dopamine D2 antagonist acting at the chemoreceptor trigger zone
C) It is a histamine H1 antagonist that blocks the cortical anticipatory pathway
D) It is an NK1 antagonist that blocks substance P in the vomiting center
E) It is a competitive muscarinic M1 receptor antagonist acting on vestibular nucleus neurons, interrupting the vestibular afferent pathway to the vomiting center
ANSWER: E
Rationale:
Scopolamine is a competitive antagonist at muscarinic M1 receptors on vestibular nucleus neurons, interrupting the vestibular afferent pathway to the vomiting center; because motion sickness is driven by vestibular input, blocking this pathway makes it the most effective single agent.
Option A: Option A describes 5-HT3 antagonists, which target the peripheral serotonin pathway dominant in acute CINV rather than the vestibular pathway.
Option B: Option B describes dopamine D2 antagonists acting at the CTZ.
Option C: Option C misidentifies the mechanism as H1 blockade of a cortical pathway; while antihistamines do help vestibular nausea, scopolamine acts through muscarinic blockade of the vestibular pathway, not a cortical one.
Option D: Option D describes NK1 antagonists targeting delayed CINV, not motion sickness.
9. Prucalopride was developed as a successor to cisapride, an earlier 5-HT4 agonist withdrawn from the market. Which property is the critical discriminator between the two agents?
A) Prucalopride is a dopamine D2 antagonist, whereas cisapride was a 5-HT4 agonist
B) Prucalopride is a selective, high-affinity 5-HT4 agonist with no significant cardiac hERG channel affinity and does not prolong the QTc, whereas non-selective cisapride blocked hERG channels and caused fatal ventricular arrhythmias
C) Prucalopride blocks hERG channels more potently than cisapride, making it more arrhythmogenic
D) Prucalopride and cisapride have identical cardiac safety profiles, and cisapride was withdrawn for hepatotoxicity
E) Prucalopride is a motilin receptor agonist, whereas cisapride was a muscarinic agonist
ANSWER: B
Rationale:
The critical discriminator is cardiac safety arising from receptor selectivity. Prucalopride is a selective, high-affinity 5-HT4 agonist with no significant affinity for cardiac hERG (human ether-a-go-go-related gene) channels, so it does not prolong the QTc interval. Cisapride, a non-selective 5-HT4 agonist, blocked hERG channels and caused fatal ventricular arrhythmias, which led to its withdrawal; prucalopride was designed specifically to retain prokinetic 5-HT4 activity without that cardiac liability.
Option A: Option A is incorrect: both agents are 5-HT4 agonists, not D2 antagonists.
Option C: Option C inverts the hERG relationship.
Option D: Option D is incorrect because the two differ markedly in cardiac safety and cisapride was withdrawn for arrhythmia, not hepatotoxicity.
Option E: Option E is incorrect because it misassigns motilin and muscarinic mechanisms to drugs that act at 5-HT4 receptors.
10. The chemoreceptor trigger zone (CTZ) and the vomiting center serve distinct roles in the emetic reflex. Which statement correctly distinguishes their functions?
A) The CTZ generates the coordinated motor output of emesis, whereas the vomiting center merely samples the blood
B) Both structures lie outside the blood-brain barrier and perform identical sampling functions
C) The CTZ is located in the cerebral cortex and mediates anticipatory nausea, whereas the vomiting center lies in the spinal cord
D) The CTZ, in the area postrema outside the blood-brain barrier, samples blood and cerebrospinal fluid for emetogens, whereas the vomiting center (a central pattern generator in the dorsal vagal complex, including the nucleus tractus solitarius) integrates afferent inputs and generates the coordinated motor output of emesis
E) The vomiting center samples bloodborne toxins, whereas the CTZ integrates vestibular and cortical inputs to trigger vomiting
ANSWER: D
Rationale:
The CTZ (chemoreceptor trigger zone), located in the area postrema outside the blood-brain barrier, samples blood and cerebrospinal fluid for emetogenic substances and relays signals onward. The vomiting center, better described as a central pattern generator in the dorsal vagal complex including the nucleus tractus solitarius (NTS), integrates convergent afferent inputs (from the CTZ, vestibular system, gut vagal afferents, and cortex) and generates the coordinated motor sequence of emesis.
Option A: Option A reverses the two roles.
Option B: Option B is incorrect because the integrating vomiting center is not an outside-the-barrier sampling site.
Option C: Option C is incorrect because it misplaces both structures anatomically.
Option E: Option E reverses the sampling and integrating roles.
11. When aprepitant is combined with dexamethasone in an antiemetic regimen, the dexamethasone dose is adjusted. Which statement correctly describes the direction of the interaction and the resulting adjustment?
A) Aprepitant induces the CYP3A4-mediated metabolism of dexamethasone, lowering its levels, so the dexamethasone dose must be increased
B) Aprepitant has no effect on dexamethasone metabolism, so no dose change is needed
C) Aprepitant inhibits CYP3A4, raising dexamethasone plasma concentrations, so the dexamethasone dose is reduced by approximately half
D) Aprepitant displaces dexamethasone from plasma proteins, so the dexamethasone dose is reduced to prevent toxicity
E) Aprepitant blocks the glucocorticoid receptor, so the dexamethasone dose must be increased to maintain effect
ANSWER: C
Rationale:
Aprepitant is a moderate inhibitor of CYP3A4, and because dexamethasone is a CYP3A4 substrate, co-administration raises dexamethasone plasma concentrations; the dexamethasone dose is therefore reduced by approximately 50% to account for the increased exposure.
Option A: Option A states the wrong direction: aprepitant inhibits rather than induces the metabolism of dexamethasone, so levels rise and the dose is decreased.
Option B: Option B is incorrect because a clinically meaningful interaction does exist.
Option D: Option D is incorrect: the mechanism is CYP3A4 inhibition, not protein-binding displacement.
Option E: Option E is incorrect because aprepitant is an NK1 antagonist and does not block the glucocorticoid receptor.
12. Dronabinol occupies a specific niche among antiemetics. Which description most accurately captures its pharmacology and clinical role?
A) A synthetic delta-9-tetrahydrocannabinol that is a partial agonist at CB1 cannabinoid receptors, FDA-approved for chemotherapy-induced nausea refractory to conventional antiemetics and for AIDS-related anorexia, and classified as a Schedule III controlled substance
B) A selective 5-HT3 antagonist used first-line for acute CINV
C) A dopamine D2 antagonist used first-line for postoperative nausea
D) An NK1 antagonist that is the preferred agent for delayed CINV
E) A motilin receptor agonist used primarily for gastroparesis
ANSWER: A
Rationale:
Dronabinol is a synthetic delta-9-tetrahydrocannabinol (delta-9-THC) that acts as a partial agonist at CB1 (cannabinoid receptor type 1) receptors in the CNS, producing antiemetic and orexigenic (appetite-stimulating) effects. It is FDA-approved for CINV (chemotherapy-induced nausea and vomiting) refractory to conventional antiemetics and for anorexia and weight loss in AIDS, is a Schedule III controlled substance, and is used as a rescue agent rather than first-line therapy.
Option B: Option B misidentifies it as a 5-HT3 antagonist.
Option C: Option C misidentifies it as a D2 antagonist.
Option D: Option D misidentifies it as an NK1 antagonist.
Option E: Option E misidentifies it as a motilin agonist; dronabinol acts at CB1 receptors and is not a gastroparesis prokinetic.
13. Haloperidol has an established role as an antiemetic in certain settings. Which statement best describes this role and its pharmacological basis?
A) It is a 5-HT4 agonist used to accelerate gastric emptying in gastroparesis
B) It is a butyrophenone dopamine D2 antagonist used at low doses (0.5 to 2 mg) for antiemesis in palliative care and for opioid-induced nausea, effective via chemoreceptor trigger zone D2 blockade with a lower sedation burden than phenothiazines at antiemetic doses
C) It is an NK1 antagonist used to prevent delayed CINV
D) It is a motilin agonist used for acute gastroparetic crises
E) It is a muscarinic antagonist used primarily for motion sickness
ANSWER: B
Rationale:
Haloperidol is a butyrophenone dopamine D2 receptor antagonist used at low doses (0.5 to 2 mg) as an antiemetic in palliative care and for opioid-induced nausea; it is effective through chemoreceptor trigger zone (CTZ) D2 blockade and has a lower sedation burden than phenothiazines at antiemetic doses.
Option A: Option A misidentifies it as a 5-HT4 agonist.
Option C: Option C misidentifies it as an NK1 antagonist.
Option D: Option D misidentifies it as a motilin agonist (the role of erythromycin).
Option E: Option E misidentifies it as a muscarinic antagonist (the role of scopolamine); haloperidol acts through D2 blockade, not muscarinic blockade.
14. Where domperidone is available and used for gastroparesis, specific safety precautions are required because of its principal toxicity. Which precaution set correctly matches that toxicity?
A) Monitor for extrapyramidal symptoms and obtain periodic involuntary-movement assessments
B) Monitor liver function tests at baseline and monthly because of hepatotoxicity risk
C) Monitor serum prolactin and counsel about galactorrhea as the dose-limiting concern
D) Monitor complete blood counts for agranulocytosis as the principal risk
E) Obtain a baseline ECG to confirm an acceptable QTc, use the lowest effective dose, and avoid concurrent QTc-prolonging drugs, because domperidone prolongs the QTc through hERG potassium channel blockade
ANSWER: E
Rationale:
Domperidone's principal safety concern is QTc prolongation from cardiac hERG (human ether-a-go-go-related gene) potassium channel blockade, with an associated risk of serious ventricular arrhythmias. Appropriate precautions are to obtain a baseline ECG to confirm an acceptable QTc, use the lowest effective dose, and avoid concurrent QTc-prolonging drugs.
Option A: Option A describes precautions relevant to metoclopramide (which crosses the blood-brain barrier and causes extrapyramidal effects), not domperidone, which is largely CNS-sparing.
Option B: Option B is incorrect: hepatotoxicity is not domperidone's dose-limiting toxicity.
Option C: Option C describes hyperprolactinemia, which is more characteristic of metoclopramide's central D2 blockade and is not the principal arrhythmia-related precaution.
Option D: Option D is incorrect because agranulocytosis is not the characteristic risk of domperidone.
15. The diagnosis of gastroparesis rests on a specific objective criterion. Which statement correctly states it?
A) Endoscopic finding of a mechanical gastric outlet obstruction
B) Symptoms of nausea and early satiety alone, without any objective test
C) Demonstration of accelerated gastric emptying on a radiolabeled meal study
D) Gastric emptying scintigraphy showing retention of more than 10% of a standardized radiolabeled solid meal at 4 hours, with mechanical obstruction excluded
E) A fasting serum gastrin level above the upper limit of normal
ANSWER: D
Rationale:
Gastroparesis is diagnosed by gastric emptying scintigraphy demonstrating retention of greater than 10% of a standardized radiolabeled solid meal at 4 hours after ingestion, with mechanical obstruction excluded by endoscopy or imaging; it is by definition delayed (not accelerated) emptying in the absence of obstruction.
Option A: Option A describes mechanical obstruction, which must be excluded rather than demonstrated to make this diagnosis.
Option B: Option B is incorrect because objective documentation of delayed emptying is required, not symptoms alone.
Option C: Option C states the opposite of the defining finding: emptying is delayed, not accelerated.
Option E: Option E is incorrect because serum gastrin is not a diagnostic criterion for gastroparesis.
16. The metoclopramide black box warning limiting use to 12 weeks is grounded in a specific neuropharmacological mechanism. Which statement correctly identifies that mechanism and its clinical consequence?
A) Acute dose-dependent QTc prolongation that resolves promptly on discontinuation
B) Striatal dopamine D2 receptor upregulation and sensitization after prolonged blockade, producing tardive dyskinesia that is often irreversible even after the drug is stopped
C) Reversible hyperprolactinemia that fully normalizes within 12 weeks regardless of continued use
E) Depletion of striatal dopamine stores that recovers immediately on discontinuation
ANSWER: B
Rationale:
Tardive dyskinesia from metoclopramide results from dopamine D2 receptor upregulation and sensitization in the striatum after prolonged D2 blockade; it is characterized by repetitive involuntary orofacial and limb movements and is often irreversible even after the drug is discontinued, which is the basis for the FDA black box 12-week limit.
Option A: Option A misidentifies the mechanism as QTc prolongation, which is not the basis for this warning.
Option C: Option C is incorrect: although hyperprolactinemia does occur, it is not the basis for the 12-week limit, and the warning concerns the often-irreversible movement disorder.
Option D: Option D misidentifies the mechanism as hepatocyte injury.
Option E: Option E is incorrect: the mechanism is receptor upregulation from blockade, not depletion of dopamine stores.
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