1. The chemoreceptor trigger zone (CTZ) is a key target for antiemetic drugs because circulating emetogenic substances such as chemotherapy agents, opioids, and uremic toxins can activate it directly from the bloodstream. Which anatomical feature of the CTZ explains this property?
A) It is located within the cerebral cortex, where it integrates conscious perception of nausea
B) It lies in the area postrema and is situated outside the blood-brain barrier (BBB), the protective barrier that normally restricts entry of bloodborne substances into brain tissue
C) It is the only CNS site that lacks dopamine D2 receptors (the receptor subtype blocked by many antiemetics)
D) It receives its blood supply directly from the hepatic portal circulation rather than the systemic arterial circulation
E) It is protected by an unusually dense blood-brain barrier that selectively concentrates emetogenic toxins
ANSWER: B
Rationale:
The CTZ (chemoreceptor trigger zone) is located in the area postrema on the floor of the fourth ventricle, and its defining anatomical feature is that it lies outside the blood-brain barrier (BBB). Because of this, circulating emetogenic substances including chemotherapy agents, uremic toxins, opioids, and digoxin can directly activate CTZ neurons without needing to cross the BBB. The CTZ is densely populated with dopamine D2 receptors, serotonin 5-HT3 receptors, and neurokinin NK1 receptors, making it the primary pharmacological target for antiemetics.
Option A: Option A is incorrect because the CTZ is in the area postrema of the medulla, not the cerebral cortex; cortical input is a separate afferent pathway for anticipatory nausea.
Option C: Option C is incorrect because the CTZ is in fact richly populated with D2 receptors rather than lacking them.
Option D: Option D is incorrect because the CTZ samples systemic blood and cerebrospinal fluid, not portal venous blood.
Option E: Option E inverts the correct concept: the CTZ is notable for lying outside the BBB, not for having an unusually dense one.
2. A patient receiving moderately emetogenic chemotherapy is given ondansetron for prophylaxis against acute nausea and vomiting. By what mechanism does ondansetron produce its antiemetic effect?
A) Agonism at motilin receptors on gastric smooth muscle, accelerating gastric emptying
B) Antagonism at neurokinin NK1 receptors, blocking substance P signaling in the delayed phase of emesis
C) Partial agonism at CB1 cannabinoid receptors in the vomiting center
D) Antagonism at serotonin 5-HT3 receptors on vagal afferent terminals in the gut and at the nucleus tractus solitarius (NTS, a brainstem relay nucleus for visceral afferents)
E) Antagonism at dopamine D2 receptors in the chemoreceptor trigger zone
ANSWER: D
Rationale:
Ondansetron is a 5-HT3 receptor antagonist (5-HT3RA). It blocks serotonin 5-HT3 receptors on vagal afferent terminals in the gut wall and in the NTS (nucleus tractus solitarius), interrupting the peripheral serotonin-mediated afferent signal generated when chemotherapy causes enterochromaffin cell serotonin release. This makes 5-HT3RAs the cornerstone of acute chemotherapy-induced nausea and vomiting (CINV) prophylaxis (within 24 hours) and highly effective for postoperative nausea and vomiting.
Option A: Option A describes the mechanism of low-dose erythromycin, a motilin receptor agonist prokinetic.
Option B: Option B describes the NK1 receptor antagonists such as aprepitant, which target the delayed phase of CINV.
Option C: Option C describes dronabinol, a CB1 partial agonist.
Option E: Option E describes dopamine D2 antagonist antiemetics such as prochlorperazine or metoclopramide; ondansetron has no significant D2 activity.
3. The U.S. Food and Drug Administration (FDA) requires a black box warning on metoclopramide stating that it should not be used for longer than 12 weeks. What adverse effect is the basis for this duration limit?
A) Tardive dyskinesia (repetitive involuntary orofacial and limb movements), which is often irreversible and whose risk rises with duration of use and cumulative dose
B) Irreversible hepatic failure from cumulative hepatocyte toxicity
C) QTc prolongation leading to torsades de pointes
D) Pulmonary fibrosis from chronic alveolar inflammation
E) Aplastic anemia from bone marrow suppression
ANSWER: A
Rationale:
Metoclopramide carries an FDA black box warning limiting use to no more than 12 weeks because of the risk of tardive dyskinesia (TD). TD is characterized by repetitive involuntary orofacial and limb movements and results from dopamine D2 receptor upregulation and sensitization in the striatum after prolonged D2 blockade; it is often irreversible even after the drug is discontinued, and the risk increases with both duration of use and total cumulative dose.
Option C: Option C (QTc prolongation) is a real concern for some other antiemetics such as ondansetron, droperidol, and domperidone but is not the basis for the metoclopramide 12-week limit.
Option B: Option B (hepatic failure) is incorrect because metoclopramide does not characteristically cause hepatotoxicity and this is not the reason for the warning.
Option D: Option D (pulmonary fibrosis) is incorrect because this toxicity is not associated with metoclopramide.
Option E: Option E (aplastic anemia) is incorrect because metoclopramide does not cause bone marrow suppression and this is not the basis for the black box warning.
4. In guideline-concordant prophylaxis for highly emetogenic chemotherapy, which agent is added to a 5-HT3 receptor antagonist and an NK1 receptor antagonist as a standard adjunct that improves complete response rates?
A) Scopolamine
B) Erythromycin
C) Dexamethasone, a corticosteroid used as an antiemetic adjunct in virtually all multimodal antiemetic regimens
D) Prucalopride
E) Domperidone
ANSWER: C
Rationale:
Dexamethasone is used as an antiemetic adjunct in virtually all multimodal antiemetic regimens. Its exact antiemetic mechanism is incompletely understood (proposed mechanisms include reduced brainstem prostaglandin synthesis, reduced serotonin release from enterochromaffin cells, and reduced blood-brain barrier permeability to emetogens), but its efficacy as an add-on agent in both acute and delayed CINV (chemotherapy-induced nausea and vomiting) is well established, consistently improving complete response rates by roughly 15 to 25 percentage points when added to 5-HT3RA-based regimens.
Option A: Option A (scopolamine) is a muscarinic antagonist used for motion sickness, not a standard CINV adjunct.
Option B: Option B (erythromycin) is a motilin receptor agonist prokinetic, not an antiemetic adjunct.
Option D: Option D (prucalopride) is a 5-HT4 agonist for chronic constipation.
Option E: Option E (domperidone) is a peripherally selective D2 antagonist used as a prokinetic, not a component of the standard three-drug HEC antiemetic regimen.
5. A patient prone to motion sickness on long sea voyages asks for the most effective single agent to prevent it. Which drug, and by what mechanism, is the best choice?
A) Ondansetron, by blocking 5-HT3 receptors on vagal afferents
B) Aprepitant, by blocking NK1 receptors in the CNS
C) Metoclopramide, by blocking dopamine D2 receptors in the CTZ
D) Dexamethasone, by reducing brainstem prostaglandin synthesis
E) Scopolamine, by competitively antagonizing muscarinic M1 receptors 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. It is the most effective single agent for motion sickness and is also used for nausea from labyrinthine dysfunction; the transdermal patch (about 1 mg over 72 hours) applied behind the ear provides sustained muscarinic blockade. Motion sickness is driven by the vestibular afferent input to the vomiting center, so agents targeting that pathway are most effective.
Option A: Option A (ondansetron) targets the peripheral serotonin/vagal pathway that dominates acute CINV, not vestibular nausea.
Option B: Option B (aprepitant) targets substance P/NK1 in delayed CINV.
Option C: Option C (metoclopramide) acts at CTZ D2 receptors and on gut motility, not the vestibular pathway.
Option D: Option D (dexamethasone) is a CINV/PONV adjunct without specific antivertiginous activity.
6. Aprepitant is added to antiemetic regimens specifically to address the delayed phase of chemotherapy-induced nausea and vomiting. What is its mechanism of action?
A) Antagonism at serotonin 5-HT3 receptors on vagal afferents
B) Antagonism at neurokinin NK1 receptors, blocking substance P (a neuropeptide mediating delayed emesis) signaling in the CNS and periphery
C) Antagonism at muscarinic M1 receptors in the vestibular nuclei
D) Agonism at serotonin 5-HT4 receptors on myenteric neurons
E) Antagonism at dopamine D2 receptors in the chemoreceptor trigger zone
ANSWER: B
Rationale:
Aprepitant is an NK1 receptor antagonist (NK1RA). It blocks substance P binding at NK1 receptors in the CNS and periphery, targeting the delayed phase of CINV (chemotherapy-induced nausea and vomiting). Substance P is a neuropeptide released in response to chemotherapy cytotoxicity, and its receptor-mediated effects correlate with delayed emesis peaking at 48 to 72 hours and persisting through day 5.
Option A: Option A describes the 5-HT3 antagonists (ondansetron and similar), which cover the acute phase.
Option C: Option C describes scopolamine's vestibular muscarinic mechanism.
Option D: Option D describes 5-HT4 agonist prokinetics such as prucalopride.
Option E: Option E describes dopamine D2 antagonist antiemetics; aprepitant has no D2 activity.
7. Low-dose erythromycin is used as a prokinetic agent in acute gastroparesis. Which mechanism accounts for its prokinetic effect?
A) Blockade of dopamine D2 receptors in the enteric nervous system
B) Antagonism of serotonin 5-HT3 receptors on vagal afferents
C) Selective agonism at serotonin 5-HT4 receptors in the colon
D) Agonism at motilin receptors on gastric smooth muscle and enteric neurons, mimicking the hormone motilin and driving phase III contractions of the migrating motor complex
E) Competitive antagonism at muscarinic M1 receptors
ANSWER: D
Rationale:
At subantimicrobial doses, erythromycin acts as a motilin receptor agonist on gastric smooth muscle and enteric neurons, mimicking the endogenous hormone motilin that drives the phase III interdigestive contractions of the migrating motor complex (MMC). It produces powerful antral contractions and is among the most potent prokinetics available. Its main limitation is tachyphylaxis from motilin receptor downregulation within days to weeks, so it is most useful for acute gastroparesis rather than chronic management.
Option A: Option A describes metoclopramide and domperidone (D2 antagonists).
Option B: Option B describes 5-HT3 antagonist antiemetics, which are not prokinetic.
Option C: Option C describes prucalopride, a colonic 5-HT4 agonist.
Option E: Option E describes scopolamine's mechanism, which is antiemetic rather than prokinetic.
8. Domperidone, like metoclopramide, is a dopamine D2 receptor antagonist, yet it does not cause the extrapyramidal adverse effects (drug-induced movement disorders) seen with metoclopramide. What explains this difference?
A) Domperidone does not readily cross the blood-brain barrier because it is a substrate for P-glycoprotein (P-gp, an efflux transporter that pumps the drug back out of the CNS), so it does not appreciably block central D2 receptors
B) Domperidone is a partial agonist rather than a full antagonist at central D2 receptors
C) Domperidone selectively blocks 5-HT3 receptors instead of D2 receptors in the brain
D) Domperidone is rapidly metabolized in the CNS before it can act on striatal neurons
E) Domperidone binds only presynaptic D2 autoreceptors, which do not mediate extrapyramidal effects
ANSWER: A
Rationale:
Domperidone is a D2 antagonist that does not readily cross the blood-brain barrier (BBB) because it is a substrate for P-glycoprotein (P-gp) efflux transport at the BBB. This peripheral selectivity means it produces prokinetic and antiemetic effects through CTZ D2 blockade (the area postrema lies outside the BBB) and enteric D2 blockade, without the central extrapyramidal effects seen with metoclopramide, which crosses the BBB freely. Its major safety concern is instead QTc prolongation via hERG channel blockade.
Option B: Option B is incorrect: domperidone is a D2 antagonist, not a partial agonist, and partial agonism would not explain the absence of EPS.
Option C: Option C is incorrect because domperidone acts at D2, not 5-HT3, receptors.
Option D: Option D is incorrect: the basis is P-gp exclusion at the BBB, not CNS metabolism.
Option E: Option E is incorrect; the selectivity is anatomical (BBB exclusion), not a preference for presynaptic autoreceptors.
9. Which statement correctly describes the regulatory status of pharmacological options for gastroparesis in the United States?
A) Erythromycin is FDA-approved for chronic outpatient management of gastroparesis
B) Domperidone is the FDA-approved first-line agent for gastroparesis in the United States
C) Metoclopramide is the only FDA-approved drug for gastroparesis in the United States and remains first-line despite its tardive dyskinesia risk
D) Prucalopride is FDA-approved specifically for diabetic gastroparesis
E) No drug is FDA-approved for gastroparesis; all therapy is off-label
ANSWER: C
Rationale:
Metoclopramide is the only FDA-approved drug for gastroparesis in the United States and remains the first-line pharmacological agent despite its tardive dyskinesia risk, which is why it must be used at the lowest effective dose for the shortest period not exceeding 12 weeks.
Option A: Option A is incorrect: erythromycin is used off-label and is limited by tachyphylaxis, useful mainly for acute exacerbations rather than chronic management, and is not FDA-approved for this indication.
Option B: Option B is incorrect: domperidone is not approved for sale in the United States and is available only through expanded-access pathways.
Option D: Option D is incorrect: prucalopride is approved for chronic idiopathic constipation, not gastroparesis.
Option E: Option E is incorrect because metoclopramide does hold FDA approval for this indication.
10. Metoclopramide and domperidone accelerate gastric emptying in part through dopamine D2 receptor blockade within the gut wall. What is the immediate downstream consequence of blocking these enteric D2 receptors?
A) Direct stimulation of motilin receptors on gastric smooth muscle
B) Inhibition of acetylcholine release from the myenteric plexus, slowing antral contractions
C) Increased serotonin release from enterochromaffin cells, activating 5-HT3 afferents
D) Relaxation of the pyloric sphincter through nitric oxide release
E) Disinhibition of cholinergic neurotransmission, because D2 signaling normally inhibits acetylcholine release from the myenteric plexus, so its blockade increases antral contractile amplitude and improves antroduodenal coordination
ANSWER: E
Rationale:
D2 receptor signaling on enteric neurons inhibits acetylcholine (ACh) release from the myenteric plexus. Blocking these receptors therefore disinhibits cholinergic neurotransmission, increasing antral contractile amplitude, improving antroduodenal coordination, and accelerating gastric emptying.
Option B: Option B states the opposite of the correct effect: D2 blockade increases (not inhibits) ACh release and speeds contractions.
Option A: Option A describes the separate motilin agonist mechanism of erythromycin, not D2 blockade.
Option C: Option C describes the emetogenic serotonin pathway, which prokinetic D2 blockade does not produce.
Option D: Option D describes nitrergic pyloric relaxation, which is not the mechanism by which D2 antagonists enhance motility.
11. The FDA recommends against single intravenous doses of ondansetron greater than 32 mg. Which adverse effect drives this dosing restriction, and what is its mechanism?
A) Serotonin syndrome from excessive central serotonergic activity
B) QTc prolongation (lengthening of the heart's electrical recovery interval) through blockade of the cardiac hERG potassium channel, which can predispose to torsades de pointes
C) Extrapyramidal symptoms from central dopamine D2 blockade
D) Hepatotoxicity from saturation of CYP3A4 metabolism
E) Profuse diarrhea from enteric 5-HT3 receptor blockade
ANSWER: B
Rationale:
The principal adverse effect of clinical importance with 5-HT3 antagonists is QTc (corrected QT interval) prolongation through cardiac hERG (human ether-a-go-go-related gene) channel blockade. Ondansetron causes dose-dependent QTc prolongation, and the FDA recommends against single IV doses greater than 32 mg because that dose was associated with significant QTc prolongation on ECG monitoring; the concern is greatest with pre-existing QTc prolongation, hypokalemia, hypomagnesemia, or concurrent QTc-prolonging drugs.
Option A: Option A is incorrect: 5-HT3 antagonists block, rather than enhance, serotonergic transmission and are not a typical cause of serotonin syndrome.
Option C: Option C is incorrect because ondansetron has no significant D2 activity and does not cause EPS.
Option D: Option D is incorrect: hepatotoxicity is not the basis for the dose cap.
Option E: Option E inverts a real effect: 5-HT3 blockade tends to cause constipation, not diarrhea, and is not the reason for the dose limit.
12. Among the 5-HT3 receptor antagonists, palonosetron is often preferred in regimens intended to cover delayed chemotherapy-induced nausea and vomiting. Which pharmacological properties account for this preference?
A) It additionally blocks NK1 receptors, giving it dual-phase coverage
B) It is the only 5-HT3 antagonist that crosses the blood-brain barrier
C) It is a prodrug activated slowly in hepatic tissue, prolonging its onset
D) It has a substantially longer half-life (approximately 40 hours) and higher receptor binding affinity than first-generation agents, with demonstrated superior efficacy against delayed CINV compared with ondansetron
E) It is administered as a continuous infusion, maintaining steady plasma levels
ANSWER: D
Rationale:
Palonosetron has a substantially longer half-life (approximately 40 hours) and higher 5-HT3 receptor binding affinity than first-generation 5-HT3 antagonists, and it has demonstrated superior efficacy in preventing delayed CINV compared with ondansetron in clinical trials. It also has minimal hERG affinity, so it does not cause clinically significant QTc prolongation at therapeutic doses.
Option A: Option A is incorrect: palonosetron is a selective 5-HT3 antagonist and does not itself block NK1 receptors (the fixed-dose NEPA combination adds netupitant for that).
Option B: Option B is incorrect; its advantage is pharmacokinetic, not BBB penetration.
Option C: Option C is incorrect: palonosetron is not a slowly activated prodrug.
Option E: Option E is incorrect because its sustained effect comes from its intrinsic long half-life and high affinity, not from continuous infusion.
13. A patient on chronic metoclopramide develops galactorrhea (inappropriate milk production) and amenorrhea (absence of menstrual periods). Which mechanism explains these findings?
A) Blockade of D2 receptors in the tuberoinfundibular pathway, which removes dopamine's tonic inhibition of pituitary lactotrophs and raises prolactin secretion
B) Direct agonism at pituitary prolactin receptors
C) Stimulation of hypothalamic thyrotropin-releasing hormone secretion
D) Blockade of hepatic prolactin clearance, raising circulating levels
E) Estrogen receptor agonism in breast and pituitary tissue
ANSWER: A
Rationale:
Metoclopramide blocks D2 receptors in the tuberoinfundibular pathway, removing dopamine's tonic inhibition of lactotrophs (prolactin-secreting cells) in the anterior pituitary and thereby increasing prolactin secretion. The resulting hyperprolactinemia causes galactorrhea, amenorrhea, and sexual dysfunction with chronic use.
Option B: Option B is incorrect: metoclopramide does not agonize prolactin receptors; it disinhibits prolactin release upstream.
Option C: Option C is incorrect; the mechanism is loss of dopaminergic inhibition, not TRH stimulation, though TRH can raise prolactin in other contexts.
Option D: Option D is incorrect: the effect is increased secretion, not reduced hepatic clearance.
Option E: Option E is incorrect because metoclopramide has no estrogenic activity.
14. Acute chemotherapy-induced nausea and vomiting (within the first 24 hours) is driven primarily by a specific peripheral pathway. Which sequence correctly describes it?
A) Substance P release activating central NK1 receptors, which then signal to the dorsal vagal complex
B) Direct chemotherapy activation of cortical centers producing anticipatory emesis
C) Chemotherapy-induced damage causes enterochromaffin cells in the gut mucosa to release serotonin, which acts on 5-HT3 receptors on vagal afferent terminals, generating signals that travel via the vagus nerve to the nucleus tractus solitarius
D) Vestibular nucleus activation transmitting via muscarinic pathways to the vomiting center
E) Motilin-driven migrating motor complex contractions stimulating mechanoreceptors
ANSWER: C
Rationale:
The peripheral limb of acute CINV begins when chemotherapy-induced cellular damage causes enterochromaffin (EC) cells in the gut mucosa to release serotonin. That serotonin acts on 5-HT3 receptors on vagal afferent terminals in the gut wall, generating action potentials that travel via the vagus nerve to the nucleus tractus solitarius (NTS) and initiate emesis. This serotonin/5-HT3 pathway is the primary mechanism of acute CINV within the first 24 hours and is the target of 5-HT3 antagonists.
Option A: Option A describes the substance P/NK1 pathway, which mediates the delayed (not acute) phase.
Option B: Option B describes cortical anticipatory nausea, a separate input.
Option D: Option D describes the vestibular pathway relevant to motion sickness.
Option E: Option E describes a prokinetic motility mechanism, not the emetogenic afferent pathway of acute CINV.
15. Low-dose erythromycin is effective for acute gastroparetic exacerbations but loses efficacy when used continuously over several weeks. What accounts for this loss of prokinetic effect over time?
A) Induction of CYP3A4 that accelerates erythromycin metabolism
B) Development of antibiotic resistance in gut flora
C) Progressive hepatic accumulation causing dose reduction
D) Competitive displacement from motilin receptors by endogenous motilin
E) Tachyphylaxis (diminishing response with repeated dosing) caused by downregulation of motilin receptors within days to weeks of continuous administration
ANSWER: E
Rationale:
Erythromycin's principal limitation as a prokinetic is tachyphylaxis: motilin receptor downregulation occurs within days to weeks of continuous administration, substantially reducing prokinetic efficacy. This is why it is most useful for acute gastroparesis or post-surgical ileus rather than chronic outpatient management.
Option A: Option A is incorrect: although erythromycin inhibits CYP3A4, the loss of prokinetic effect is due to receptor downregulation, not accelerated self-metabolism.
Option B: Option B is incorrect because the prokinetic effect is a motilin receptor action unrelated to antimicrobial activity or flora resistance.
Option C: Option C is incorrect; hepatic accumulation is not the mechanism.
Option D: Option D is incorrect: the effect is receptor downregulation, not displacement by endogenous motilin.
16. Cisapride, an earlier 5-HT4 agonist, was withdrawn because it caused fatal ventricular arrhythmias, whereas prucalopride was developed to retain prokinetic activity without that cardiac liability. What pharmacological distinction underlies prucalopride's improved safety?
A) Prucalopride acts on motilin receptors rather than 5-HT4 receptors, avoiding cardiac effects
B) Prucalopride is a selective, high-affinity 5-HT4 agonist with no significant affinity for the cardiac hERG channel, so it does not prolong the QTc interval, unlike non-selective cisapride
C) Prucalopride is administered only intravenously, allowing tight monitoring that prevents arrhythmia
D) Prucalopride blocks rather than activates 5-HT4 receptors, eliminating proarrhythmic signaling
E) Prucalopride is rapidly cleared by the kidney before reaching cardiac tissue
ANSWER: B
Rationale:
Prucalopride is a selective, high-affinity 5-HT4 receptor agonist that, unlike the non-selective cisapride, has no significant affinity for cardiac hERG (human ether-a-go-go-related gene) channels and therefore does not prolong the QTc interval. Cisapride's hERG blockade produced fatal ventricular arrhythmias and led to its withdrawal; prucalopride was developed specifically to retain prokinetic 5-HT4 activity without that cardiac liability.
Option A: Option A is incorrect: prucalopride acts at 5-HT4 receptors, not motilin receptors.
Option C: Option C is incorrect: prucalopride is an oral agent, and the safety advantage is receptor selectivity, not a route-based monitoring effect.
Option D: Option D is incorrect: it is a 5-HT4 agonist, not an antagonist, and agonism is what produces its prokinetic colonic effect.
Option E: Option E is incorrect; renal clearance is not the basis for its cardiac safety.
17. When aprepitant is added to an antiemetic regimen that also contains dexamethasone, the dexamethasone dose is typically reduced by about half. What is the pharmacological basis for this dose adjustment?
A) Aprepitant displaces dexamethasone from plasma protein binding, increasing free drug
B) Aprepitant and dexamethasone compete for renal tubular secretion, raising dexamethasone levels
C) Aprepitant induces CYP3A4, lowering dexamethasone exposure and requiring a higher dose
D) Aprepitant is a moderate inhibitor of CYP3A4 (a major drug-metabolizing enzyme), so it raises plasma concentrations of the CYP3A4 substrate dexamethasone, and the dexamethasone dose is reduced to compensate for the increased exposure
E) Aprepitant blocks dexamethasone's glucocorticoid receptor, requiring a higher dose to maintain effect
ANSWER: D
Rationale:
Aprepitant is both a CYP3A4 substrate and a moderate CYP3A4 inhibitor over its standard dosing course. Because dexamethasone is metabolized by CYP3A4, aprepitant raises dexamethasone plasma concentrations, so the dexamethasone antiemetic dose is reduced by approximately 50% (to roughly 8 mg) when co-administered with aprepitant to account for the increased exposure.
Option C: Option C states the opposite direction: aprepitant inhibits the CYP3A4-mediated metabolism of dexamethasone, raising rather than lowering its levels, so the dexamethasone dose is decreased and not increased. Aprepitant does separately induce CYP2C9, which lowers warfarin levels, but that interaction affects warfarin rather than dexamethasone.
Option A: Option A is incorrect: the interaction is metabolic CYP3A4 inhibition, not protein-binding displacement.
Option B: Option B is incorrect; renal secretion competition is not the mechanism.
Option E: Option E is incorrect: aprepitant is an NK1 antagonist and does not block the glucocorticoid receptor.
18. A patient with Parkinson disease develops nausea and delayed gastric emptying. Which antiemetic/prokinetic consideration is most important in selecting therapy for this patient?
A) Metoclopramide should be avoided because it crosses the blood-brain barrier and blocks central D2 receptors, which can worsen the motor dysfunction of Parkinson disease
B) Metoclopramide is preferred because its central D2 blockade improves parkinsonian tremor
C) Ondansetron is contraindicated because 5-HT3 blockade worsens parkinsonian rigidity
D) Domperidone must be avoided because it readily crosses the blood-brain barrier and aggravates parkinsonism
E) Scopolamine is contraindicated because muscarinic blockade worsens Parkinson motor symptoms
ANSWER: A
Rationale:
Metoclopramide crosses the blood-brain barrier and blocks central D2 receptors; in Parkinson disease, where dopaminergic signaling is already deficient, this additional D2 blockade can worsen motor dysfunction, so metoclopramide should be avoided.
Option B: Option B states the opposite of the truth: central D2 blockade aggravates, not improves, parkinsonism.
Option C: Option C is incorrect: ondansetron lacks D2 activity and is not contraindicated for this reason.
Option D: Option D is incorrect because domperidone does not readily cross the BBB (it is a P-gp substrate), which is precisely why it is often the preferred D2 antagonist in parkinsonian patients.
Option E: Option E is incorrect: anticholinergic agents do not characteristically worsen Parkinson motor symptoms and have historically been used for tremor, so scopolamine is not contraindicated on that basis.
19. A patient does well during the first 24 hours after highly emetogenic chemotherapy but develops nausea and vomiting peaking on days 2 to 3. Which mediator and receptor are chiefly responsible for this delayed-phase emesis?
A) Serotonin acting on peripheral 5-HT3 receptors on vagal afferents
B) Dopamine acting on D2 receptors in the chemoreceptor trigger zone
C) Substance P acting on neurokinin NK1 receptors, the mediator of delayed-phase CINV that peaks at roughly 48 to 72 hours and persists through day 5
D) Histamine acting on H1 receptors in the vestibular pathway
E) Acetylcholine acting on muscarinic M1 receptors in the vestibular nuclei
ANSWER: C
Rationale:
The delayed phase of CINV (chemotherapy-induced nausea and vomiting) is mediated by substance P acting at neurokinin NK1 receptors. Substance P is released in response to chemotherapy cytotoxicity, and its receptor-mediated effects correlate with delayed emesis that peaks at 48 to 72 hours and persists through day 5, which is why NK1 antagonists such as aprepitant target this phase.
Option A: Option A describes the acute-phase (first 24 hours) serotonin/5-HT3 pathway, not the delayed phase.
Option B: Option B describes the dopaminergic CTZ pathway targeted by D2 antagonists, not the principal driver of the delayed phase.
Option D: Option D describes a histaminergic H1 vestibular pathway relevant to motion sickness, not chemotherapy-induced delayed emesis.
Option E: Option E describes a muscarinic M1 vestibular pathway relevant to motion sickness, not the delayed phase of CINV.
20. Droperidol, a butyrophenone antiemetic once widely used for postoperative nausea and vomiting, became far less commonly used after the FDA issued a black box warning in 2001. What was the basis for that warning?
A) Irreversible tardive dyskinesia with single perioperative doses
B) Fatal respiratory depression in young children
C) Acute hepatic failure
D) Neuroleptic malignant syndrome at antiemetic doses
E) QTc prolongation with risk of fatal ventricular arrhythmias
ANSWER: E
Rationale:
Droperidol received an FDA black box warning in 2001 for QTc prolongation and the risk of fatal arrhythmias, which led to a substantial decline in its use; it retains a limited role at low doses (0.625 to 1.25 mg IV) for PONV where QTc risk is judged acceptable.
Option A: Option A is incorrect: tardive dyskinesia from prolonged D2 blockade is the basis for the metoclopramide warning, not droperidol's PONV warning.
Option B: Option B describes the promethazine black box warning in children under age 2 (fatal respiratory depression), not droperidol.
Option C: Option C is incorrect; hepatic failure is not the basis for the droperidol warning.
Option D: Option D is incorrect: while neuroleptic malignant syndrome is a recognized risk of dopamine antagonists generally, the specific 2001 black box warning concerned QTc prolongation and arrhythmia.
21. In a patient with longstanding diabetes who develops gastroparesis, which pathophysiological process best explains the impaired gastric emptying?
A) Mechanical gastric outlet obstruction from diabetic microangiopathy
B) Chronic hyperglycemia damages the interstitial cells of Cajal (the gastric pacemaker cells) and injures enteric neurons and the vagus nerve through autonomic neuropathy, causing loss of coordinated antral contractility and pyloric relaxation
C) Autoimmune destruction of gastric parietal cells reducing acid secretion
D) Overgrowth of gastric smooth muscle producing pyloric hypertrophy
In diabetic gastroparesis, chronic hyperglycemia damages the interstitial cells of Cajal (ICC), which generate gastric pacemaker activity, and injures enteric neurons and the vagus nerve via autonomic neuropathy. The resulting loss of coordinated antral contractility and pyloric relaxation impairs gastric emptying and produces the symptom complex of nausea, early satiety, and postprandial fullness. By definition, gastroparesis is delayed emptying in the absence of mechanical obstruction, so a fixed structural blockage such as gastric outlet obstruction is excluded, and the deficit is one of disordered neuromuscular motility rather than a physical barrier.
Option A: Option A is incorrect.
Option C: Option C describes autoimmune atrophic gastritis affecting acid and intrinsic factor, not the motility defect of gastroparesis.
Option D: Option D is incorrect: the problem is impaired contractility and pacemaker function, not muscle overgrowth or pyloric hypertrophy.
Option E: Option E inverts the pathophysiology: motility is reduced through ICC and neural injury, not driven by motilin excess.
22. A patient on chronic warfarin (an anticoagulant monitored by the international normalized ratio, INR) receives an aprepitant-containing antiemetic regimen with chemotherapy. Which interaction should be anticipated and monitored?
A) Aprepitant inhibits warfarin metabolism, raising the INR and increasing bleeding risk
B) Aprepitant displaces warfarin from albumin, transiently raising the INR
C) Aprepitant blocks vitamin K epoxide reductase, potentiating warfarin's effect
D) Aprepitant induces CYP2C9 (the enzyme that metabolizes warfarin), which can lower warfarin plasma concentrations and reduce the INR, so the INR should be monitored
E) Aprepitant has no clinically relevant interaction with warfarin
ANSWER: D
Rationale:
Aprepitant induces CYP2C9, the primary enzyme metabolizing the more active S-enantiomer of warfarin. This induction can reduce warfarin plasma concentrations and lower the INR, so the INR should be monitored in patients on warfarin receiving aprepitant-containing antiemetic regimens.
Option A: Option A states the wrong direction: aprepitant induces (rather than inhibits) the relevant warfarin-metabolizing pathway, tending to lower the INR.
Option B: Option B is incorrect: the interaction is enzyme induction, not protein-binding displacement.
Option C: Option C is incorrect: aprepitant does not inhibit vitamin K epoxide reductase (that is warfarin's own target).
Option E: Option E is incorrect because a clinically meaningful CYP2C9-mediated interaction does exist and warrants INR monitoring.
This Web-based pharmacology and disease-based integrated teaching site is based on reference materials that are believed reliable and consistent with standards accepted at the time of development.
Possibility of error and on-going research and development in medical sciences do not allow assurance that the information contained herein is in every respect accurate or complete.
Users should confirm the information contained herein with other sources.
This site should only be considered as a teaching aid for undergraduate and graduate biomedical education and is intended only as a teaching site.
Information contained here should not be used for patient management and should not be used as a substitute for consultation with practicing medical professionals.
Users of this website should check the product information sheet included in the package of any drug they plan to administer to be certain that the information contained in this site is accurate and that changes have not been made in the recommended dose or in the contraindications for administration.
Medical or other information thus obtained should not be used as a substitute for consultation with practicing medical or scientific or other professionals.