Antiemetics — MCQs
Damage to pneumotaxic center along with vagus nerve causes which type of respiration?
Which of the following is the primary neurotransmitter involved in nausea and vomiting associated with chemotherapy?
Which antiemetic phenothiazine has labyrinthine suppressant activity and is used for vertigo?
A medical student presented to the ED with protracted vomiting. For this he was given an anti-emetic drug following which he developed abnormal posturing. Which of the following is the most likely drug to be given to the patient?
How do 5-HT3 receptor antagonists like ondansetron work to prevent nausea and vomiting?
Which of the following is the FIRST-LINE antiemetic drug most commonly used for post-operative nausea and vomiting (PONV) prophylaxis?
What is the primary use of the combination of atropine and diphenoxylate?
Which of the following steroids possesses maximum glucocorticoid activity?
A 56-year-old woman has nausea due to chemotherapy for breast cancer. Droperidol is effective in reducing nausea because it blocks which of the following?
All of the following drugs cross the blood-brain barrier, EXCEPT:
Antiemetics Indian Medical PG Practice Questions and MCQs
Question 1: Damage to pneumotaxic center along with vagus nerve causes which type of respiration?
- A. Cheyne-Stokes breathing
- B. Deep and slow breathing
- C. Shallow and rapid breathing
- D. Apneustic breathing (Correct Answer)
Explanation: ***Apneustic breathing*** - Damage to the **pneumotaxic center** prevents the normal inhibition of inspiration, leading to **prolonged inspiratory gasps**. - **Vagal nerve damage** further removes the inhibitory feedback from the lungs, exacerbating the inspiratory "holds" characteristic of apneustic breathing. *Cheyne-Stokes breathing* - This pattern is characterized by a **crescendo-decrescendo pattern** of breathing, interspersed with periods of **apnea**. - It is often associated with conditions like **heart failure**, stroke, or severe neurological damage, not specifically the pneumotaxic center and vagus nerve. *Deep and slow breathing* - This pattern can be seen in conditions like **Kussmaul breathing** (due to metabolic acidosis) or as a compensatory mechanism. - It does not directly result from the combined damage of the **pneumotaxic center** and the **vagus nerve**. *Shallow and rapid breathing* - This pattern is commonly seen in restrictive lung diseases, anxiety, or pain, where tidal volume is decreased and respiratory rate increased. - It does not reflect the **prolonged inspiration** that would result from a compromised pneumotaxic center and vagal input.
Question 2: Which of the following is the primary neurotransmitter involved in nausea and vomiting associated with chemotherapy?
- A. Dopamine
- B. Acetylcholine
- C. GABA
- D. Serotonin (Correct Answer)
Explanation: ***Serotonin*** - **Serotonin (5-HT)**, particularly acting on **5-HT3 receptors**, is a major neurotransmitter mediating chemotherapy-induced nausea and vomiting (CINV). - Chemotherapeutic agents can damage **enterochromaffin cells** in the gastrointestinal tract, leading to the release of serotonin, which then stimulates vagal afferents and the **chemoreceptor trigger zone (CTZ)**. *Dopamine* - **Dopamine (D2 receptors)** plays a role in nausea and vomiting, particularly in the **chemoreceptor trigger zone (CTZ)**. - While dopamine antagonists can be used as antiemetics, **serotonin** is considered the primary neurotransmitter in CINV due to the direct impact of chemotherapy on serotonin release. *Acetylcholine* - **Acetylcholine** is involved in motion sickness and is targeted by **anticholinergic antiemetics (e.g., scopolamine)**. - Its primary role in CINV is less significant compared to serotonin, which has a more direct link to the mechanisms of chemotherapy. *GABA* - **GABA (gamma-aminobutyric acid)** is the main inhibitory neurotransmitter in the brain and can reduce anxiety and modulate vomiting. - While **benzodiazepines**, which enhance GABAergic activity, are used as adjuncts in CINV to reduce **anticipatory nausea** and anxiety, GABA itself is not the primary mediator of the emetic response to chemotherapy.
Question 3: Which antiemetic phenothiazine has labyrinthine suppressant activity and is used for vertigo?
- A. Prochlorperazine
- B. Promethazine (Correct Answer)
- C. Cinnarizine
- D. Hyoscine
Explanation: ***Promethazine*** - Promethazine is a **phenothiazine derivative** with strong **antihistaminic (H1)** properties, making it highly effective for **labyrinthine suppression** and treatment of vertigo. - It is widely used for **motion sickness, vertigo, and nausea** associated with vestibular disturbances. - Its mechanism combines **dopamine D2 receptor antagonism** (phenothiazine effect) with potent **antihistaminic** and **anticholinergic** actions that specifically suppress vestibular function. - The antihistaminic component is particularly important for labyrinthine suppressant activity. *Prochlorperazine* - While prochlorperazine is a **phenothiazine antiemetic**, it is primarily used for severe nausea and vomiting (migraine, postoperative, chemotherapy-induced). - It has predominantly **dopamine D2 antagonist** activity at the chemoreceptor trigger zone (CTZ) but weaker antihistaminic properties compared to promethazine. - Less commonly used specifically for vertigo compared to promethazine due to weaker vestibular suppressant effects. *Cinnarizine* - While effective for vertigo, cinnarizine is an **antihistamine** and **calcium channel blocker**, not a phenothiazine. - It acts on the **vestibular system** by inhibiting calcium influx into vestibular sensory cells. *Hyoscine* - Hyoscine (**scopolamine**) is an **anticholinergic drug** (not a phenothiazine) effective for motion sickness and some forms of vertigo. - Works by blocking **muscarinic acetylcholine receptors** in the vestibular nuclei.
Question 4: A medical student presented to the ED with protracted vomiting. For this he was given an anti-emetic drug following which he developed abnormal posturing. Which of the following is the most likely drug to be given to the patient?
- A. Ondansetron
- B. Domperidone
- C. Dexamethasone
- D. Metoclopramide (Correct Answer)
Explanation: ***Metoclopramide*** - **Metoclopramide** is a **dopamine D2 receptor antagonist** that can cause **extrapyramidal symptoms (EPS)**, such as abnormal posturing (dystonia), due to its central action. - This adverse effect is more common with higher doses or in susceptible individuals, and the scenario directly describes it as a consequence of the antiemetic. *Ondansetron* - **Ondansetron** is a **5-HT3 receptor antagonist** primarily used for nausea and vomiting, particularly chemotherapy-induced. - It works **peripherally and centrally** but its side effect profile does not typically include extrapyramidal symptoms like abnormal posturing. *Domperidone* - **Domperidone** is also a **dopamine D2 receptor antagonist**, but it has **limited penetration across the blood-brain barrier**. - Due to its predominantly peripheral action, it causes **fewer central nervous system side effects**, including extrapyramidal symptoms, compared to metoclopramide. *Dexamethasone* - **Dexamethasone** is a **corticosteroid** with antiemetic properties, often used in conjunction with other antiemetics, especially in chemotherapy. - Its mechanism is not related to dopamine receptors, and it **does not typically cause extrapyramidal symptoms or abnormal posturing**.
Question 5: How do 5-HT3 receptor antagonists like ondansetron work to prevent nausea and vomiting?
- A. Blocking serotonin receptors in the chemoreceptor trigger zone (Correct Answer)
- B. Inhibiting dopamine release
- C. Decreasing gastric acid secretion
- D. Reducing gastrointestinal motility
Explanation: ***Blocking serotonin receptors in the chemoreceptor trigger zone*** - 5-HT3 receptor antagonists like **ondansetron** work primarily by blocking **serotonin (5-HT3) receptors** found in the **chemoreceptor trigger zone (CTZ)** and on afferent vagal nerves in the gastrointestinal tract. - This action prevents serotonin, a key mediator of nausea and vomiting, from stimulating these receptors and initiating the **emetic reflex**. *Inhibiting dopamine release* - **Dopamine antagonists**, such as metoclopramide or prochlorperazine, act by blocking **D2 dopamine receptors** in the CTZ, which is a different mechanism of action. - While dopamine can contribute to nausea and vomiting, 5-HT3 antagonists do not directly work by inhibiting dopamine release. *Decreasing gastric acid secretion* - Medications that decrease gastric acid secretion, such as **proton pump inhibitors (PPIs)** or **H2 blockers**, are used to treat conditions like GERD or ulcers. - This mechanism is not directly involved in the antiemetic action of 5-HT3 receptor antagonists. *Reducing gastrointestinal motility* - Some antiemetics, like **anticholinergics (e.g., scopolamine)**, can reduce gastrointestinal motility, which may help alleviate nausea. - However, 5-HT3 receptor antagonists primarily exert their antiemetic effect through receptor blockade rather than by significantly altering GI motility.
Question 6: Which of the following is the FIRST-LINE antiemetic drug most commonly used for post-operative nausea and vomiting (PONV) prophylaxis?
- A. Lorazepam
- B. Metoclopramide
- C. Promethazine
- D. Ondansetron (Correct Answer)
Explanation: ***Ondansetron*** - **Ondansetron** is a **5-HT3 receptor antagonist** and is considered a first-line agent due to its high efficacy and favorable side effect profile in preventing PONV. - It works by blocking serotonin receptors in the **chemoreceptor trigger zone** and the **gastrointestinal tract**, reducing the sensation of nausea and vomiting. *Lorazepam* - **Lorazepam** is a **benzodiazepine** primarily used for its **anxiolytic** and **sedative effects**, and sometimes as an adjunct for refractory nausea, but not as a first-line antiemetic for PONV prophylaxis. - While it can help indirectly by reducing anxiety, it does not directly target the key pathways involved in PONV as effectively as 5-HT3 antagonists. *Phenytoin* - **Phenytoin** is an **anticonvulsant** medication used to prevent seizures and has no role in the direct treatment or prophylaxis of PONV. - It primarily acts on voltage-gated sodium channels in neurons and does not possess antiemetic properties. *Metoclopramide* - **Metoclopramide** is a **dopamine D2 receptor antagonist** and a **prokinetic agent** that can be used for PONV, particularly when gastric stasis is a concern. - However, it is generally considered a second-line agent due to the risk of **extrapyramidal side effects**, especially with higher doses or prolonged use. *Promethazine* - **Promethazine** is a **first-generation antihistamine** with **antidopaminergic** and **anticholinergic properties** that can be effective for nausea and vomiting. - It is often used as a rescue antiemetic or in combination therapy, but its sedative effects and potential for extrapyramidal symptoms make it less preferable as a first-line prophylactic agent compared to ondansetron.
Question 7: What is the primary use of the combination of atropine and diphenoxylate?
- A. Iridocyclitis
- B. Nausea and vomiting
- C. Glaucoma
- D. Diarrhea (Correct Answer)
Explanation: ***Diarrhea*** - The combination of **diphenoxylate** (an opioid receptor agonist) and a **small amount of atropine** is primarily used to treat diarrhea. - **Diphenoxylate** reduces gut motility, while **atropine** is added to discourage abuse by causing unpleasant anticholinergic side effects at higher doses. *Glaucoma* - **Atropine** is contraindicated in patients with **glaucoma** due to its mydriatic effect, which can worsen angle-closure glaucoma. - The combination is not used to treat glaucoma; glaucoma treatments aim to reduce intraocular pressure. *Iridocyclitis* - **Atropine** can be used in iridocyclitis as a **cycloplegic agent** to prevent synechiae formation and relieve pain. - However, **diphenoxylate** has no role in the treatment of iridocyclitis, making the combination inappropriate for this condition. *Nausea and vomiting* - Some anticholinergic drugs can be used for nausea and vomiting, such as **scopolamine**, but **atropine** is not a primary antiemetic in this context. - **Diphenoxylate**'s primary action is on gut motility for diarrhea, not specifically for nausea and vomiting.
Question 8: Which of the following steroids possesses maximum glucocorticoid activity?
- A. Prednisolone
- B. Aldosterone
- C. Dexamethasone (Correct Answer)
- D. Cortisol
Explanation: ***Dexamethasone*** - **Dexamethasone** is a synthetic glucocorticoid with high potency, making it one of the steroids with the **maximum glucocorticoid activity** [1], [2]. - It exhibits a much longer duration of action and significantly greater anti-inflammatory effects compared to natural glucocorticoids like cortisol [2]. *Prednisolone* - **Prednisolone** is a synthetic glucocorticoid that has approximately four times the anti-inflammatory potency of cortisol [1]. - While potent, it does not reach the glucocorticoid activity levels of dexamethasone. *Cortisol* - **Cortisol** is the body's primary natural glucocorticoid, involved in stress response and metabolism [2]. - Its glucocorticoid activity serves as a baseline for comparing the potencies of other synthetic corticosteroids [2]. *Aldosterone* - **Aldosterone** is primarily a mineralocorticoid, not a glucocorticoid, with its main role being the regulation of electrolyte and water balance [2]. - It possesses minimal to no glucocorticoid activity.
Question 9: A 56-year-old woman has nausea due to chemotherapy for breast cancer. Droperidol is effective in reducing nausea because it blocks which of the following?
- A. Glucocorticoid receptors in the vomiting center
- B. Dopamine receptors in the CTZ (Correct Answer)
- C. ACh receptors in the periphery
- D. 5-HT3 receptors in the CTZ
Explanation: **Dopamine receptors in the CTZ** - Droperidol is a **butyrophenone antipsychotic** that acts as an **antidopaminergic agent**, primarily targeting **D2 dopamine receptors**. - Its antiemetic effect is mainly due to blocking these **dopamine receptors in the chemoreceptor trigger zone (CTZ)**, which is involved in initiating the vomiting reflex. *Glucocorticoid receptors in the vomiting center* - **Glucocorticoids** like dexamethasone are used as antiemetics, but they act via **glucocorticoid receptors**, not through dopamine receptor blockade. - Their mechanism involves inhibiting prostaglandin synthesis and inflammation, reducing the release of serotonin. *ACh receptors in the periphery* - Drugs that block **acetylcholine (ACh) receptors** (e.g., scopolamine) are used for motion sickness, but they are not the primary mechanism of action for droperidol. - **Anticholinergics** typically exert their effects on the vestibular system and peripheral muscarinic receptors. *5-HT 2 receptors in the CTZ* - While some antiemetics (e.g., **ondansetron**) block **serotonin (5-HT3) receptors**, droperidol's primary action is not on **5-HT2 receptors**. - **Serotonin antagonists** are particularly effective for chemotherapy-induced nausea and vomiting as chemotherapy often releases serotonin from enterochromaffin cells.
Question 10: All of the following drugs cross the blood-brain barrier, EXCEPT:
- A. Physostigmine
- B. Atropine
- C. Neostigmine (Correct Answer)
- D. Lignocaine
Explanation: ***Neostigmine*** - As a **quaternary ammonium compound**, neostigmine carries a permanent positive charge, making it highly **hydrophilic** and unable to readily cross the **blood-brain barrier (BBB)**. - Its inability to cross the BBB means its effects are primarily limited to the **peripheral nervous system**, particularly at the neuromuscular junction for conditions like myasthenia gravis, or in the gut for paralytic ileus. *Physostigmine* - Physostigmine is a **tertiary amine** that is **lipid-soluble** at physiological pH, allowing it to easily cross the **blood-brain barrier** and exert central nervous system effects. - It is used to treat **central anticholinergic syndrome** because it can reverse the central effects of anticholinergic drugs. *Atropine* - Atropine is a **tertiary amine** that is also **lipid-soluble** and readily crosses the **blood-brain barrier**, leading to significant central nervous system effects such as sedation, excitation, or even delirium at higher doses. - Its ability to cross the BBB contributes to its wide range of systemic anticholinergic effects, including those on the brain. *Lignocaine* - Lignocaine (lidocaine) is a **tertiary amine local anesthetic** that is highly **lipid-soluble** and can readily cross the **blood-brain barrier**. - Its entry into the CNS is responsible for its potential side effects such as **seizures, dizziness, and central nervous system depression** when absorbed systemically.
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