Emetics and antiemetics – mechanism and clinical use
Understanding emetics and antiemetics is vital for B. Pharm students preparing for clinical pharmacy and therapeutics. This concise guide covers pharmacological mechanisms (CTZ, vomiting centre, 5-HT3, D2, NK1, H1, M1 receptors), major drug classes (5-HT3 antagonists, dopamine antagonists, NK1 antagonists, antihistamines, anticholinergics, cannabinoids, corticosteroids, emetics like apomorphine and ipecac), pharmacokinetics, adverse effects (EPS, QT prolongation, sedation, anticholinergic effects), and key clinical uses (CINV, motion sickness, postoperative nausea, poisoning). Emphasis is placed on drug interactions, pregnancy considerations, and evidence-based combination therapy. Now let’s test your knowledge with 30 MCQs on this topic.
Q1. Which brain region acts as the primary chemoreceptor trigger zone (CTZ) for detecting blood-borne emetic agents?
- Vomiting centre in the medulla oblongata
- Area postrema
- Vestibular nucleus
- Hypothalamus
Correct Answer: Area postrema
Q2. Ondansetron primarily prevents chemotherapy-induced nausea by antagonizing which receptor?
- Dopamine D2 receptor
- Neurokinin-1 receptor
- 5-HT3 receptor
- Histamine H1 receptor
Correct Answer: 5-HT3 receptor
Q3. Which antiemetic is a selective NK1 receptor antagonist used for preventing delayed CINV and interacts with CYP3A4?
- Metoclopramide
- Aprepitant
- Dexamethasone
Correct Answer: Aprepitant
Q4. Metoclopramide’s antiemetic effect is mainly due to antagonism at which receptor in the CTZ?
- 5-HT3 receptor
- D2 receptor
- NK1 receptor
- H1 receptor
Correct Answer: D2 receptor
Q5. Which antiemetic has a significant risk of extrapyramidal symptoms (EPS) and tardive dyskinesia with long-term use?
- Domperidone
- Ondansetron
- Metoclopramide
- Scopolamine
Correct Answer: Metoclopramide
Q6. Which antiemetic is preferred for motion sickness due to its antimuscarinic action?
- Scopolamine
- Ondansetron
- Aprepitant
- Dronabinol
Correct Answer: Scopolamine
Q7. Which statement best describes the mechanism of 5-HT3 antagonists in preventing vomiting?
- They block central D2 receptors in the CTZ.
- They inhibit peripheral and central 5-HT3 receptors on vagal afferents and in the CTZ.
- They antagonize H1 receptors in the vestibular system.
- They activate NK1 receptors to reduce emesis.
Correct Answer: They inhibit peripheral and central 5-HT3 receptors on vagal afferents and in the CTZ.
Q8. Which antiemetic is an effective prokinetic agent that accelerates gastric emptying via 5-HT4 agonism?
- Ondansetron
- Metoclopramide
- Promethazine
- Palonosetron
Correct Answer: Metoclopramide
Q9. Which of the following antiemetics is associated with QT prolongation and should be used cautiously with other QT-prolonging drugs?
- Ondansetron
- Domperidone
- Scopolamine
- Meclizine
Correct Answer: Ondansetron
Q10. Which emetic drug acts as a dopamine agonist at the CTZ and is used to induce vomiting in certain settings?
- Ipecac syrup
- Apomorphine
- Activated charcoal
- Metoclopramide
Correct Answer: Apomorphine
Q11. In chemotherapy-induced nausea and vomiting (CINV), which combination is commonly used for high emetic risk regimens?
- 5-HT3 antagonist + NK1 antagonist + dexamethasone
- Metoclopramide + scopolamine
- Antihistamine + antimuscarinic
- Dronabinol alone
Correct Answer: 5-HT3 antagonist + NK1 antagonist + dexamethasone
Q12. Which antihistamine is commonly used for vertigo and motion sickness with less sedation compared to promethazine?
- Meclizine
- Diphenhydramine
- Prochlorperazine
- Ondansetron
Correct Answer: Meclizine
Q13. Domperidone differs from metoclopramide because it:
- Causes more EPS due to central D2 blockade
- Does not cross the blood–brain barrier significantly, so causes fewer CNS effects
- Is a 5-HT3 antagonist used for CINV
- Is primarily an NK1 antagonist
Correct Answer: Does not cross the blood–brain barrier significantly, so causes fewer CNS effects
Q14. Which corticosteroid is frequently used as an adjunctive antiemetic in CINV with unclear precise mechanism?
- Hydrocortisone
- Dexamethasone
- Prednisone
- Fludrocortisone
Correct Answer: Dexamethasone
Q15. Which antiemetic class is most effective for preventing acute phase chemotherapy nausea mediated by serotonin release from enterochromaffin cells?
- NK1 antagonists
- 5-HT3 antagonists
- Dopamine antagonists
- Anticholinergics
Correct Answer: 5-HT3 antagonists
Q16. Which antiemetic can be useful in refractory CINV and stimulates appetite, but may cause euphoria and dysphoria?
- Dronabinol (cannabinoid)
- Ondansetron
- Scopolamine
- Metoclopramide
Correct Answer: Dronabinol (cannabinoid)
Q17. Which of the following is a contraindication or caution for using syrup of ipecac as an emetic?
- Ingestion of a small, non-toxic amount of household cleaner
- Patient with depressed level of consciousness or caustic ingestion
- Recent ingestion of food
- Use within 30 minutes of ingestion only
Correct Answer: Patient with depressed level of consciousness or caustic ingestion
Q18. Palonosetron differs from first-generation 5-HT3 antagonists because it has:
- Shorter half-life and more QT risk
- Higher affinity and longer half-life with efficacy in delayed CINV
- Primary action as a D2 antagonist
- Major antimuscarinic effects
Correct Answer: Higher affinity and longer half-life with efficacy in delayed CINV
Q19. Which receptor blockade is primarily responsible for motion-sickness related nausea and is targeted by antihistamines and antimuscarinics?
- NK1 receptor
- 5-HT3 receptor
- H1 and M1 receptors in the vestibular system
- D2 receptors in the CTZ
Correct Answer: H1 and M1 receptors in the vestibular system
Q20. Which adverse effect is most characteristic of dopamine D2 antagonists used as antiemetics?
- Anticholinergic dry mouth and blurred vision
- Extrapyramidal symptoms such as acute dystonia
- Severe QT prolongation in all patients
- Respiratory depression
Correct Answer: Extrapyramidal symptoms such as acute dystonia
Q21. Aprepitant’s clinical role in CINV is primarily due to blockade of which peptide receptor?
- Substance P – NK1 receptor
- Serotonin – 5-HT3 receptor
- Dopamine – D2 receptor
- Histamine – H1 receptor
Correct Answer: Substance P – NK1 receptor
Q22. Which antiemetic is often recommended for pregnancy-related nausea and vomiting due to a favorable safety profile?
- High-dose ondansetron as first-line
- Combination of aprepitant and dexamethasone
- Pyridoxine (vitamin B6) with or without doxylamine
- Metoclopramide as sole therapy in all cases
Correct Answer: Pyridoxine (vitamin B6) with or without doxylamine
Q23. Which of the following is the most appropriate antiemetic for postoperative nausea in a patient with a history of prolonged QT interval?
- Ondansetron
- Prochlorperazine
- Dexamethasone
- Domperidone
Correct Answer: Dexamethasone
Q24. Which antiemetic has antiemetic effects partly due to blockade of alpha-adrenergic and H1 receptors and is also sedating?
- Meclizine
- Promethazine
- Palonosetron
- Aprepitant
Correct Answer: Promethazine
Q25. In acute poisoning management, why is activated charcoal usually preferred over emetics like ipecac?
- Activated charcoal neutralizes caustic ingestions chemically.
- Activated charcoal adsorbs many toxins and has a better safety profile than inducing emesis.
- Ipecac is more effective at preventing systemic absorption.
- Activated charcoal induces vomiting more reliably.
Correct Answer: Activated charcoal adsorbs many toxins and has a better safety profile than inducing emesis.
Q26. Which antiemetic is most likely to exacerbate glaucoma because of anticholinergic effects?
- Scopolamine
- Ondansetron
- Aprepitant
- Domperidone
Correct Answer: Scopolamine
Q27. Which mechanism explains ondansetron-associated constipation in some patients?
- Peripheral 5-HT3 blockade reduces GI motility and secretion
- Central D2 blockade increases intestinal transit
- NK1 activation increases bowel motility
- Antimuscarinic activity causes diarrhea
Correct Answer: Peripheral 5-HT3 blockade reduces GI motility and secretion
Q28. Which antiemetic is contraindicated or has major warnings due to cardiac arrhythmia risk, especially with high doses or IV push?
- Ondansetron IV bolus
- Oral metoclopramide at low doses
- Pyridoxine for morning sickness
- Scopolamine patch
Correct Answer: Ondansetron IV bolus
Q29. Which statement about cannabinoid antiemetics (e.g., dronabinol) is true?
- They are first-line for acute CINV in all patients due to minimal side effects.
- They can be useful for refractory CINV and cause central psychotropic effects.
- They act primarily via 5-HT3 receptor antagonism.
- They have no effect on appetite stimulation.
Correct Answer: They can be useful for refractory CINV and cause central psychotropic effects.
Q30. Which clinical factor most strongly predicts the need for multimodal antiemetic prophylaxis in a chemotherapy patient?
- Low emetogenic risk regimen with single agent
- High emetogenic potential of the chemotherapeutic regimen
- Patient age under 18 only
- Use of antiemetics in the past only
Correct Answer: High emetogenic potential of the chemotherapeutic regimen
I am a Registered Pharmacist under the Pharmacy Act, 1948, and the founder of PharmacyFreak.com. I hold a Bachelor of Pharmacy degree from Rungta College of Pharmaceutical Science and Research. With a strong academic foundation and practical knowledge, I am committed to providing accurate, easy-to-understand content to support pharmacy students and professionals. My aim is to make complex pharmaceutical concepts accessible and useful for real-world application.
Mail- Sachin@pharmacyfreak.com