- Dexamethasone is frequently used as an adjunct antiemetic in CINV regimens. Although its mechanism is not fully understood, its efficacy is thought to be related to which of the following actions?
Answer: Inhibition of central prostaglandin synthesis.
The leading hypothesis for the antiemetic action of corticosteroids like dexamethasone is the inhibition of prostaglandin synthesis within the central nervous system. Chemotherapy can induce an inflammatory response that increases prostaglandin production, which can then contribute to nausea and vomiting. By reducing prostaglandin levels, dexamethasone helps mitigate this effect. The other options describe the mechanisms of dopamine antagonists, benzodiazepines, and cannabinoids, respectively.
- The use of the butyrophenone antiemetic droperidol has been significantly restricted due to a black box warning. This warning highlights the risk of which serious cardiovascular adverse event?
Answer: QTc prolongation and Torsades de Pointes
Droperidol carries a black box warning from the FDA regarding its potential to cause dose-dependent QTc interval prolongation, which can lead to Torsades de Pointes, a life-threatening ventricular arrhythmia. This has led to restrictions on its use, often requiring ECG monitoring before and during administration. While extrapyramidal symptoms are also a risk, the cardiovascular concern is the subject of the specific black box warning.
- A patient is receiving a multi-day chemotherapy regimen. The oncologist chooses palonosetron over ondansetron. What pharmacokinetic property of palonosetron makes it particularly advantageous in this setting?
Answer: It has a significantly longer plasma half-life.
Palonosetron is a second-generation 5-HT3 receptor antagonist with a much longer half-life (~40 hours) compared to first-generation agents like ondansetron (~4-6 hours). This prolonged duration of action provides extended coverage against nausea and vomiting, making it particularly effective for preventing delayed CINV, which can occur for several days after chemotherapy administration.
- The extrapyramidal symptoms, such as tardive dyskinesia, associated with long-term use of metoclopramide are caused by its antagonist action in which specific central nervous system dopamine pathway?
Answer: Nigrostriatal pathway
When you encounter questions about antipsychotic side effects, focus on understanding the four major dopamine pathways in the brain and their clinical consequences when blocked.
Metoclopramide's extrapyramidal symptoms, including tardive dyskinesia, result from dopamine receptor antagonism in the nigrostriatal pathway. This pathway connects the substantia nigra to the striatum (caudate nucleus and putamen) and is essential for controlling voluntary movement and motor coordination. When dopamine receptors here are chronically blocked, you get the characteristic movement disorders: acute dystonia, parkinsonism, akathisia, and tardive dyskinesia.
Looking at the wrong answers: B) Mesocortical pathway connects the ventral tegmental area to the prefrontal cortex and primarily affects cognitive function and negative symptoms of schizophrenia—not movement. C) Mesolimbic pathway runs from the ventral tegmental area to limbic structures and is responsible for the therapeutic antipsychotic effects (blocking this reduces positive symptoms like hallucinations), not motor side effects. D) Tuberoinfundibular pathway connects the hypothalamus to the pituitary gland; blocking dopamine here causes prolactin elevation and galactorrhea, not movement disorders.
Study tip: Remember "NMMT" for the four dopamine pathways: Nigrostriatal (movement disorders), Mesocortical (cognitive effects), Mesolimbic (therapeutic antipsychotic effects), Tuberoinfundibular (prolactin effects). This framework applies to all dopamine antagonists, whether antipsychotics or antiemetics like metoclopramide.
- A patient about to begin his third cycle of chemotherapy reports severe anxiety and nausea upon entering the cancer center, well before the infusion begins. Which medication is most appropriate to manage this specific type of nausea and vomiting?
Answer: Lorazepam
This patient is experiencing anticipatory nausea and vomiting (ANV), a conditioned response triggered by environmental cues associated with previous chemotherapy. ANV is mediated by higher cortical centers and is best managed with anxiolytics. Lorazepam, a benzodiazepine, is the standard of care for ANV due to its anxiolytic, sedative, and amnestic properties. Standard antiemetics like granisetron (5-HT3 antagonist), aprepitant (NK1 antagonist), and dexamethasone are not effective for this indication.
- A patient receiving refractory CINV is treated with dronabinol. This agent's therapeutic effect is primarily mediated by agonism at which receptor type?
Answer: Cannabinoid CB1 receptor
Dronabinol is a synthetic form of delta-9-tetrahydrocannabinol (THC), the primary psychoactive component of cannabis. Its antiemetic effects are mediated through the activation (agonism) of cannabinoid type 1 (CB1) receptors in the central nervous system, including areas associated with the control of nausea and vomiting. It is typically reserved for patients who have failed to respond to standard antiemetic therapies.
- An 82-year-old patient with Parkinson's disease develops nausea due to a viral illness. Which of the following antiemetics is most likely to exacerbate his parkinsonian motor symptoms?
Answer: Prochlorperazine
Parkinson's disease is characterized by a deficiency of dopamine in the nigrostriatal pathway. Prochlorperazine is a potent dopamine D2 receptor antagonist. By blocking the remaining dopamine receptors, it can significantly worsen the motor symptoms of Parkinson's disease (e.g., tremor, rigidity, bradykinesia). Ondansetron, dimenhydrinate, and aprepitant do not act primarily on dopamine receptors and are safer choices in this population.
- A 10-week pregnant woman presents with moderate nausea and vomiting of pregnancy (NVP) that has not responded to dietary modifications. According to current guidelines, what is the most appropriate first-line pharmacologic treatment?
Answer: Combination of pyridoxine and doxylamine
The first-line pharmacologic treatment for nausea and vomiting of pregnancy recommended by the American College of Obstetricians and Gynecologists (ACOG) is the combination of pyridoxine (vitamin B6) and doxylamine (an antihistamine). This combination has a strong safety record and proven efficacy. While other agents like ondansetron, prochlorperazine, and metoclopramide may be used for more severe or refractory cases (hyperemesis gravidarum), they are considered second- or third-line options.
- A patient taking a daily SSRI for depression undergoes surgery and receives a high dose of an intravenous antiemetic for PONV. Shortly after, she develops agitation, myoclonus, and hyperreflexia. While multiple factors may contribute to postoperative delirium, which antiemetic has the theoretical potential to interact with her SSRI through serotonergic mechanisms?
Answer: Ondansetron
While serotonin syndrome from ondansetron and SSRI combination is rare and controversial, ondansetron is the only agent listed that directly interacts with the serotonin system. Ondansetron blocks 5-HT3 receptors, and in theory, this could contribute to altered serotonergic signaling when combined with an SSRI. In practice, this interaction is not well-established clinically, but ondansetron remains the only serotonergic agent among the choices. Droperidol and metoclopramide are dopamine antagonists, and aprepitant is an NK1 antagonist.
- A patient receiving a standard three-drug prophylaxis (palonosetron, fosaprepitant, dexamethasone) for CINV experiences breakthrough vomiting on day 3. The physician wants to add a rescue medication with a different mechanism of action. Which of the following would be an appropriate choice?
Answer: Oral prochlorperazine
The patient's prophylactic regimen already provides maximal blockade of the 5-HT3 (palonosetron) and NK1 (fosaprepitant) pathways. Adding another agent from the same class (granisetron or more palonosetron/fosaprepitant) is unlikely to be effective. The most appropriate strategy for breakthrough CINV is to add an agent with a different mechanism. Prochlorperazine, a dopamine D2 receptor antagonist, provides a distinct mechanism of action and is a standard choice for rescue therapy.
- A patient preparing for a deep-sea fishing trip requests medication for motion sickness. Which of the following agents is a first-line therapy for this indication but is generally ineffective for chemotherapy-induced nausea?
Answer: Scopolamine
Motion sickness is primarily mediated by the vestibular system, which utilizes histaminic (H1) and muscarinic (M1) pathways. Scopolamine, a muscarinic receptor antagonist, is highly effective for preventing motion sickness. In contrast, chemotherapy-induced nausea is primarily mediated by the release of serotonin (acting on 5-HT3 receptors) from enterochromaffin cells and substance P (acting on NK1 receptors). Therefore, drugs like ondansetron and aprepitant are effective for CINV but not motion sickness, while scopolamine is effective for motion sickness but not CINV.
- A patient receiving chemotherapy is prescribed a three-drug antiemetic regimen of fosaprepitant, ondansetron, and dexamethasone. Fosaprepitant is a known moderate inhibitor of CYP3A4, and dexamethasone is a CYP3A4 substrate. What adjustment is required when these drugs are co-administered?
Answer: The dose of dexamethasone should be empirically reduced.
Fosaprepitant (the prodrug of aprepitant) inhibits CYP3A4, the enzyme responsible for metabolizing dexamethasone. This inhibition leads to increased plasma concentrations and area under the curve (AUC) of dexamethasone. To avoid potential corticosteroid toxicity, the oral dose of dexamethasone is typically reduced by approximately 50% when co-administered with an NK1 antagonist like aprepitant or fosaprepitant. D is incorrect because it is inhibition, not induction. A and C are incorrect as no dose adjustment is needed for fosaprepitant or ondansetron in this context.
- A 72-year-old female with a history of long QT syndrome (baseline QTc 490 ms) is scheduled for total hip arthroplasty. She has multiple risk factors for postoperative nausea and vomiting (PONV). Which agent should be avoided for PONV prophylaxis in this patient?
Answer: Ondansetron
Ondansetron, a 5-HT3 receptor antagonist, is known to cause dose-dependent QTc interval prolongation. In a patient with pre-existing long QT syndrome, administering ondansetron would further increase the risk of developing potentially fatal arrhythmias like Torsades de Pointes. Aprepitant, dexamethasone, and scopolamine do not have a clinically significant effect on the QTc interval and are safer alternatives in this scenario.
- Compared to a first-line 5-HT3 antagonist like ondansetron, the cannabinoid antiemetic nabilone is associated with a greater incidence of which of the following?
Answer: Appetite stimulation and dysphoria
Cannabinoid receptor agonists like nabilone and dronabinol are known for their psychoactive effects, which can include euphoria, dysphoria, hallucinations, and paranoia. They are also potent appetite stimulants (orexigenic effect). These effects are not associated with 5-HT3 antagonists. Conversely, 5-HT3 antagonists are more commonly associated with headache and constipation (and QTc prolongation), while cannabinoids do not cause EPS or have a significant risk of serotonin syndrome.
- A patient with diabetic gastroparesis presents with chronic nausea and vomiting. Which antiemetic agent possesses a secondary mechanism of action that would be beneficial for the patient's underlying motility disorder?
Answer: Metoclopramide
Metoclopramide is a D2 receptor antagonist, which accounts for its antiemetic effect. However, it also acts as a 5-HT4 receptor agonist, which enhances acetylcholine release in the gut, thereby increasing upper gastrointestinal motility (a prokinetic effect). This prokinetic action is particularly beneficial for patients with delayed gastric emptying, as seen in diabetic gastroparesis. Ondansetron can cause constipation, and promethazine has anticholinergic effects that can worsen gastroparesis.
- A patient in the emergency department for an acute migraine receives an intravenous antiemetic. Thirty minutes later, she develops a fixed upward gaze, facial grimacing, and torticollis. This reaction is most characteristic of an adverse effect from which of the following drugs?
Answer: Metoclopramide
The patient is experiencing an acute dystonic reaction, a type of extrapyramidal symptom (EPS). This is a classic adverse effect of dopamine (D2) receptor antagonists, such as metoclopramide and prochlorperazine, which are commonly used for migraine-associated nausea. The reaction results from the blockade of dopamine receptors in the nigrostriatal pathway. Ondansetron does not affect dopamine receptors. Lorazepam causes sedation, and diphenhydramine (an anticholinergic) is actually used to treat acute dystonic reactions.
- In addition to its antiemetic effects, promethazine's clinical profile is heavily influenced by its potent antagonism of which other receptors, leading to its most common side effects?
Answer: Histamine H1 and Muscarinic M1 receptors
Promethazine is a first-generation phenothiazine. While its primary antiemetic action is through dopamine D2 receptor blockade, it is also a very potent histamine H1 receptor antagonist and a moderate muscarinic M1 receptor antagonist. These additional actions are responsible for its prominent side effects: H1 blockade causes significant sedation, and M1 blockade causes anticholinergic effects (dry mouth, blurred vision, urinary retention).
- A patient is receiving a high-dose cisplatin regimen for cancer. The treatment plan includes ondansetron, dexamethasone, and aprepitant. What is the primary rationale for including aprepitant in this multi-drug antiemetic regimen?
Answer: To target the substance P/neurokinin-1 pathway, primarily for preventing delayed-phase emesis.
Aprepitant is a neurokinin-1 (NK1) receptor antagonist. Substance P, the natural ligand for the NK1 receptor, is a key mediator of the delayed phase of chemotherapy-induced nausea and vomiting (CINV). While 5-HT3 antagonists like ondansetron are highly effective for acute CINV, their efficacy diminishes in the delayed phase (24-120 hours post-chemotherapy). Aprepitant specifically targets this delayed mechanism, making it a crucial component of regimens for highly emetogenic chemotherapy.
- A patient is given instructions for using a transdermal scopolamine patch to prevent motion sickness during a 5-day cruise. Which instruction is most accurate and important for ensuring efficacy and safety?
Answer: Apply one patch behind the ear at least 4 hours before the cruise begins and replace it after 72 hours.
Transdermal drug delivery questions test your understanding of both pharmacokinetics and proper administration techniques. With scopolamine patches for motion sickness, timing and duration are critical for therapeutic success.
Answer A is correct because scopolamine patches require 4+ hours to achieve therapeutic blood levels through transdermal absorption. The patch must be applied well before exposure to motion, not after symptoms begin. The 72-hour replacement schedule matches the patch's designed duration of drug release, ensuring continuous prophylaxis throughout the cruise.
Answer B is dangerous because cutting transdermal patches can alter the controlled-release mechanism and lead to unpredictable drug delivery. Many patches contain drug reservoirs that would leak if cut, potentially causing overdose or underdose.
Answer C fails because scopolamine works prophylactically, not therapeutically. Once nausea begins, it's too late for effective prevention. Additionally, the inner wrist isn't the recommended application site due to differences in skin thickness and absorption rates.
Answer D involves unnecessary patch changes that waste medication and increase costs. The 24-hour schedule doesn't align with scopolamine's pharmacokinetics, and frequent removal/reapplication increases skin irritation risk without improving efficacy.
Study tip: For transdermal patch questions, always consider three key factors: proper timing relative to when the drug effect is needed, the patch's specific duration of action, and whether cutting or relocating patches affects the delivery system. Prophylactic medications like scopolamine must be started before symptoms appear, not after.
