Central Nervous System Pharmacology — MCQs

Central Nervous System Pharmacology Indian Medical PG Practice Questions and MCQs

Question 481: What is the drug of choice for the treatment of Alzheimer's disease?

A. Atropine
B. Donepezil (Correct Answer)
C. Physostigmine
D. Fluoxetine

Explanation: **Explanation:** **1. Why Donepezil is the Correct Answer:** Alzheimer’s disease is characterized by a cholinergic deficit in the brain, particularly in the hippocampus and cortex. **Donepezil** is a reversible, long-acting, and **centrally-acting selective acetylcholinesterase (AChE) inhibitor**. By inhibiting the breakdown of acetylcholine in the synaptic cleft, it increases cholinergic neurotransmission, which helps improve cognitive function and delay the progression of symptoms. It is preferred due to its once-daily dosing and better tolerability compared to older agents. **2. Why Other Options are Incorrect:** * **Atropine:** This is a muscarinic antagonist (anticholinergic). It would worsen cognitive decline and confusion in Alzheimer’s patients by further reducing cholinergic activity. * **Physostigmine:** While it is an AChE inhibitor that crosses the blood-brain barrier, it has a very short half-life and significant peripheral side effects, making it unsuitable for chronic management. It is primarily used as an antidote for atropine poisoning. * **Fluoxetine:** This is a Selective Serotonin Reuptake Inhibitor (SSRI) used for depression. While depression can coexist with Alzheimer’s, it does not treat the primary cognitive pathology. **3. NEET-PG High-Yield Clinical Pearls:** * **First-line drugs for Alzheimer’s:** Donepezil, Rivastigmine (available as a transdermal patch), and Galantamine. * **NMDA Antagonist:** **Memantine** is the drug of choice for moderate-to-severe Alzheimer’s; it acts by reducing glutamate-induced excitotoxicity. * **Side Effects:** Common side effects of AChE inhibitors include GI upset (nausea, diarrhea), bradycardia, and insomnia. * **Newer Monoclonal Antibodies:** Aducanumab and Lecanemab (targeting amyloid-beta plaques) are emerging therapies.

Question 482: Which of the following agents is not a serotonin and dopaminergic blocker?

A. Doxepin (Correct Answer)
B. Amisulpiride
C. Seindole
D. Zotepine

Explanation: The question asks to identify the drug that does **not** act as a combined serotonin (5-HT) and dopamine (D2) receptor blocker. **1. Why Doxepin is the correct answer:** Doxepin is a **Tricyclic Antidepressant (TCA)**. Its primary mechanism of action involves the inhibition of the reuptake of Norepinephrine and Serotonin (SERT and NET). While it has potent H1-antihistaminic and alpha-1 adrenergic blocking properties, it **does not significantly block dopamine receptors** [2]. Therefore, it is not classified as a serotonin-dopamine antagonist. **2. Why the other options are incorrect:** * **Amisulpiride:** This is an atypical antipsychotic. While it is primarily a D2/D3 blocker, at specific doses, it modulates serotonergic activity and is classified within the broader group of atypical agents that manage both positive and negative symptoms [1]. * **Sertindole:** This is a second-generation (atypical) antipsychotic. Its hallmark pharmacological profile is the high-affinity blockade of both **5-HT2A** and **D2** receptors [1]. * **Zotepine:** Another atypical antipsychotic that functions by blocking D2 receptors and 5-HT2 receptors [1]. It also inhibits the reuptake of norepinephrine, but its primary classification remains a serotonin-dopamine antagonist. **High-Yield Clinical Pearls for NEET-PG:** * **Atypical Antipsychotics (SDA):** Most "atypicals" (e.g., Risperidone, Ziprasidone, Zotepine) are **Serotonin-Dopamine Antagonists**. This dual blockade reduces Extrapyramidal Side Effects (EPS) compared to typical antipsychotics [1]. * **Doxepin Unique Fact:** It is one of the most potent H1 blockers available and is often used at low doses for insomnia (Silenor) [2]. * **Sertindole Warning:** It is associated with significant **QT interval prolongation**, requiring careful cardiac monitoring.

Question 483: Ketanserin is:

A. 5HT1B antagonist
B. 5HT2 antagonist (Correct Answer)
C. 5HT1A agonist
D. 5HT1D antagonist

Explanation: **Explanation:** **Ketanserin** is a selective **5-HT2 receptor antagonist** (specifically the 5-HT2A subtype). Its primary mechanism involves blocking serotonin-induced platelet aggregation and vasoconstriction. Additionally, it possesses significant **α1-adrenergic blocking properties**, which contributes to its clinical effect of lowering blood pressure. **Analysis of Options:** * **Option B (Correct):** Ketanserin is the prototypical 5-HT2 antagonist. It is used clinically in some countries as an antihypertensive agent and for treating Raynaud’s phenomenon. * **Option A & D (Incorrect):** 5-HT1B and 5-HT1D receptors are the primary targets for **Triptans** (e.g., Sumatriptan), which act as *agonists* to treat acute migraine. There is no major clinical drug categorized primarily as a 5-HT1B/D antagonist in standard NEET-PG curricula. * **Option C (Incorrect):** **Buspirone** is the classic example of a 5-HT1A partial agonist used as a non-benzodiazepine anxiolytic. **High-Yield Clinical Pearls for NEET-PG:** * **Other 5-HT2 Antagonists:** **Ritanserin** (more selective for 5-HT2 than Ketanserin) and **Ciperoheptadine** (also blocks H1 receptors; used for serotonin syndrome and as an appetite stimulant). * **Atypical Antipsychotics:** Drugs like Clozapine and Risperidone also derive their efficacy partly through 5-HT2A antagonism. * **Key Association:** If a question mentions a drug that blocks both 5-HT2 and α1 receptors to treat hypertension, think **Ketanserin**.

Question 484: Which of the following is not an analeptic agent?

A. Doxapram
B. Nikethamide
C. Doxacurium (Correct Answer)
D. Propylbucamide

Explanation: **Explanation:** **Analeptics** (Respiratory Stimulants) are drugs used to stimulate the central nervous system, particularly the respiratory and vasomotor centers in the medulla. They were historically used to treat acute respiratory failure or drug-induced CNS depression. **1. Why Doxacurium is the Correct Answer:** **Doxacurium** is a **long-acting, non-depolarizing neuromuscular blocking agent** (skeletal muscle relaxant) belonging to the benzylisoquinolinium class. Unlike analeptics, which stimulate the CNS, Doxacurium acts peripherally at the nicotinic receptors of the motor endplate to cause muscle paralysis. It has no respiratory stimulant properties; in fact, it causes respiratory paralysis as a side effect of its primary action. **2. Analysis of Incorrect Options:** * **Doxapram (Option A):** This is the most commonly used analeptic. It acts by stimulating peripheral chemoreceptors and, at higher doses, the central respiratory centers. It is used for post-operative respiratory depression. * **Nikethamide (Option B):** A traditional respiratory stimulant that acts directly on the medulla to increase the rate and depth of respiration. * **Propylbucamide (Option D):** Also known as Vanylamide, it is a respiratory stimulant occasionally mentioned in older pharmacological literature as an analeptic. **High-Yield Clinical Pearls for NEET-PG:** * **Doxapram** is the drug of choice for treating respiratory depression caused by COPD or anesthesia, but it has a narrow therapeutic index. * **Doxacurium** is notable for being one of the most potent neuromuscular blockers with minimal cardiovascular side effects (no histamine release). * **Analeptics** are largely replaced today by mechanical ventilation and specific antidotes (e.g., Naloxone for opioids, Flumazenil for benzodiazepines) due to their risk of inducing convulsions.

Question 485: What is the treatment for Subacute sclerosing panencephalitis (SSPE)?

A. Abacavir
B. Inosine pranobex (Correct Answer)
C. Glatiramer
D. Interferon

Explanation: **Explanation:** **Subacute Sclerosing Panencephalitis (SSPE)** is a rare, progressive, and fatal neurodegenerative disease caused by a persistent infection with a mutated measles virus. **Why Inosine Pranobex is Correct:** **Inosine pranobex** (also known as Methisoprinol) is the drug of choice for SSPE. It is an immunomodulatory agent that enhances T-cell function and increases the activity of natural killer cells. While it is not a cure, it has been shown to slow down the clinical progression of the disease and prolong survival in a significant number of patients. In clinical practice, it is often used in combination with intrathecal or intraventricular **Interferon-alpha**. **Analysis of Incorrect Options:** * **Abacavir (Option A):** This is a Nucleoside Reverse Transcriptase Inhibitor (NRTI) used in the treatment of HIV/AIDS. It has no role in treating measles-related complications. * **Glatiramer (Option C):** This is an immunomodulator used specifically for the management of Relapsing-Remitting Multiple Sclerosis (RRMS). It acts as a decoy for T-cells, preventing them from attacking myelin. * **Interferon (Option D):** While Interferon-alpha is used as an *adjunct* therapy (often administered intrathecally), **Inosine pranobex** remains the primary systemic treatment mentioned in standard pharmacological textbooks for SSPE management. **High-Yield Clinical Pearls for NEET-PG:** * **Etiology:** Occurs 5–10 years after a primary measles infection, usually in children who were infected before age 2. * **EEG Finding:** Characterized by **periodic, high-voltage slow-wave complexes** (Radermecker complexes). * **CSF Finding:** Presence of highly elevated titers of measles antibodies (**Oligoclonal bands**). * **Stages:** Progresses from behavioral changes to myoclonic jerks (Stage 2) and eventually to akinetic mutism.

Question 486: Which of the following is true regarding Zolpidem?

A. Acts on Benzodiazepine receptor 1 and 2
B. Action is not reversed by flumazenil
C. Sedation is less than Diazepam (Correct Answer)
D. All of the above

Explanation: Zolpidem belongs to the "Z-drugs" (Non-benzodiazepine hypnotics), which are chemically distinct from benzodiazepines (BZDs) but share a similar mechanism of action. [1] **1. Why Option C is Correct:** Zolpidem is highly selective for the **$\alpha_1$ subunit** of the $GABA_A$ receptor (BZ1 receptor). [4] This subunit primarily mediates sedation and hypnosis. Unlike Diazepam, which acts non-selectively on $\alpha_1, \alpha_2, \alpha_3,$ and $\alpha_5$ subunits, Zolpidem lacks significant anticonvulsant, muscle relaxant, and anxiolytic properties. [1] Consequently, while it is an effective hypnotic, the overall CNS depressant effect and "heaviness" of sedation are considered less than that of long-acting BZDs like Diazepam. It also causes minimal disruption to the sleep architecture (less suppression of REM sleep). **2. Why Other Options are Incorrect:** * **Option A:** Zolpidem is **selective for BZ1 ( $\alpha_1$) receptors** only. It has negligible affinity for BZ2 receptors ($\alpha_2, \alpha_3, \alpha_5$), which are responsible for anxiolysis and muscle relaxation. [4] * **Option B:** Since Zolpidem binds to the same BZD-binding site on the $GABA_A$ receptor (albeit selectively), its actions **are rapidly reversed by Flumazenil** (a competitive BZD antagonist). [3] **High-Yield Clinical Pearls for NEET-PG:** * **Drug of Choice:** Zolpidem is often preferred for the short-term treatment of **insomnia** (specifically sleep onset) due to its short half-life (~2 hours) and lack of "hangover" effects. * **Safety Profile:** It has a lower potential for tolerance and dependence compared to traditional BZDs. [1] * **Side Effects:** Can cause residual daytime somnolence and, rarely, complex sleep behaviors (sleep-walking/driving). * **Other Z-drugs:** Zaleplon (shortest acting) and Eszopiclone (longest acting, used for chronic insomnia). [2]

Question 487: A 72-year-old patient with Parkinsonism presents with swollen feet. The feet are red, tender, and very painful. Which medication, if stopped, would likely resolve these symptoms within a few days?

A. Amantadine (Correct Answer)
B. Benztropine
C. Bromocriptine
D. Levodopa

Explanation: ### Explanation The patient is presenting with **Livedo Reticularis** and **Ankle Edema**, which are classic side effects associated with **Amantadine** therapy. **1. Why Amantadine is Correct:** Amantadine is an antiviral drug used in Parkinsonism to increase dopamine release and inhibit reuptake. A unique side effect of Amantadine is **Livedo Reticularis**—a purplish, lace-like discoloration of the skin, often accompanied by **peripheral edema** (swollen, red, and painful feet). This occurs due to the depletion of catecholamines in peripheral nerve terminals, leading to local vasoconstriction and fluid extravasation. These symptoms are reversible and typically resolve within a few days to weeks after discontinuing the drug. **2. Why Incorrect Options are Wrong:** * **Benztropine:** An anticholinergic drug. Common side effects include "dry" symptoms (dry mouth, blurred vision, urinary retention, and constipation), not peripheral edema or skin discoloration. * **Bromocriptine:** An ergot-derived dopamine agonist. While it can cause erythromelalgia (red, painful extremities), it is more famously associated with **pulmonary/retroperitoneal fibrosis**. Amantadine is the more "textbook" cause for the specific presentation of livedo reticularis in NEET-PG questions. * **Levodopa:** The gold standard for Parkinson’s. Its primary side effects are GI upset (nausea/vomiting), dyskinesias, and "on-off" phenomena, but it does not typically cause localized pedal edema or livedo reticularis. **Clinical Pearls for NEET-PG:** * **Amantadine Triple Action:** Increases dopamine release, blocks dopamine reuptake, and acts as an **NMDA receptor antagonist**. * **High-Yield Side Effect:** Always associate "Livedo Reticularis" with Amantadine in the context of Parkinson’s. * **Contraindication:** Use with caution in patients with a history of heart failure, as the edema can exacerbate the condition.

Question 488: Which among the following is an early sign of magnesium toxicity?

A. Depression of deep tendon reflexes (Correct Answer)
B. Respiratory depression
C. Cardiac arrest
D. Decreased urine output

Explanation: **Explanation:** Magnesium sulfate ($MgSO_4$) is the drug of choice for managing seizures in eclampsia. However, it has a narrow therapeutic index, making the monitoring of toxicity clinically vital. **1. Why Option A is Correct:** The **depression or loss of deep tendon reflexes (DTRs)**, specifically the patellar reflex (knee-jerk), is the **earliest clinical sign** of magnesium toxicity. This occurs at serum magnesium levels of **7–10 mEq/L**. Magnesium acts as a calcium antagonist at the neuromuscular junction, inhibiting the release of acetylcholine and decreasing the sensitivity of the motor end-plate, which manifests first as areflexia. **2. Why Other Options are Incorrect:** * **B. Respiratory Depression:** This is a later and more severe sign, typically occurring when serum levels reach **10–12 mEq/L**. * **C. Cardiac Arrest:** This is a terminal event of toxicity, occurring at very high levels, usually **>15 mEq/L**. * **D. Decreased Urine Output:** This is not a *sign* of toxicity itself, but rather a **predisposing factor**. Since magnesium is excreted solely by the kidneys, oliguria leads to magnesium accumulation and subsequent toxicity. **High-Yield Clinical Pearls for NEET-PG:** * **Therapeutic Range:** 4–7 mEq/L. * **Monitoring Parameters:** To safely administer $MgSO_4$, three things must be present: (1) Intact Patellar reflex, (2) Respiratory rate >12-14/min, and (3) Urine output >30 ml/hr. * **Antidote:** 10 ml of **10% Calcium Gluconate** administered IV over 10 minutes.

Question 489: Ebstein's anomaly may be a complication of which drug when used during the first trimester of pregnancy?

A. Sodium valproate
B. Lamotrigine
C. Lithium carbonate (Correct Answer)
D. Carbamazepine

Explanation: **Explanation:** **Lithium carbonate** is the correct answer. It is a mood stabilizer used primarily for Bipolar Disorder. When administered during the **first trimester** of pregnancy, Lithium is associated with a specific cardiac teratogenic effect known as **Ebstein’s anomaly** [1]. This condition involves the "atrialization" of the right ventricle due to the downward displacement of the tricuspid valve leaflets, leading to severe tricuspid regurgitation and right heart failure [1]. **Analysis of Incorrect Options:** * **A. Sodium Valproate:** This is highly teratogenic but is primarily associated with **Neural Tube Defects (NTDs)** like spina bifida (due to interference with folate metabolism) and craniofacial abnormalities. * **B. Lamotrigine:** Generally considered one of the safest anti-epileptics during pregnancy. It is not associated with Ebstein's anomaly. * **C. Carbamazepine:** Similar to Valproate, it is associated with **Neural Tube Defects** and "Fetal Hydantoin-like syndrome" features, but not specific cardiac malformations like Ebstein’s [2]. **High-Yield Clinical Pearls for NEET-PG:** * **Risk Ratio:** While the relative risk of Ebstein’s anomaly increases with Lithium use, the absolute risk remains low (approx. 1-2 per 1,000 exposures). * **Monitoring:** If a pregnant woman must stay on Lithium, perform a **fetal echocardiogram** at 18–20 weeks. * **Lactation:** Lithium is contraindicated during breastfeeding as it is excreted in milk and can cause "Floppy Baby Syndrome" [1]. * **Other Teratogens:** Remember **Phenytoin** (Fetal Hydantoin Syndrome) and **Warfarin** (Fetal Warfarin Syndrome/Chondrodysplasia punctata).

Question 490: Tetrabenazine acts by inhibiting which of the following?

A. MAO-B
B. Vesicular monoamine transporter (Correct Answer)
C. Dopamine D2 receptors
D. COMT

Explanation: **Explanation:** **Tetrabenazine** is a reversible inhibitor of the **Vesicular Monoamine Transporter type 2 (VMAT2)**. 1. **Mechanism of Action (Why B is correct):** VMAT2 is responsible for transporting monoamines (Dopamine, Serotonin, Norepinephrine) from the cytosol into synaptic vesicles for storage. By inhibiting VMAT2, Tetrabenazine prevents the packaging of these neurotransmitters, leading to their degradation by cytosolic MAO. This results in the **depletion of monoamine stores**, particularly dopamine, in the nerve terminals. This reduction in dopamine levels is clinically useful in treating hyperkinetic movement disorders. 2. **Why other options are incorrect:** * **MAO-B (A):** Inhibitors like Selegiline or Rasagiline prevent the breakdown of dopamine; Tetrabenazine actually promotes its depletion. * **Dopamine D2 receptors (C):** While Tetrabenazine has a weak affinity for D2 receptors, its primary and potent mechanism is VMAT2 inhibition. Direct D2 blockers are typical/atypical antipsychotics (e.g., Haloperidol). * **COMT (D):** COMT inhibitors (e.g., Entacapone) are used in Parkinson’s disease to prevent the peripheral breakdown of Levodopa. **Clinical Pearls for NEET-PG:** * **Indications:** Primarily used for **Huntington’s Chorea** and other hyperkinetic disorders like Tardive Dyskinesia or Tourette syndrome. * **Side Effects:** Due to monoamine depletion, it can cause **depression**, sedation, and secondary Parkinsonism. * **Deutetrabenazine:** A newer, deuterated form of Tetrabenazine with a longer half-life and better tolerability. * **Valbenazine:** A highly selective VMAT2 inhibitor specifically approved for Tardive Dyskinesia.

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General Anesthetics

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Local Anesthetics

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Sedative-Hypnotics

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Antiepileptic Drugs

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Antiparkinsonian Drugs

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Opioid Analgesics

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Drugs of Abuse and Addiction

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Psychostimulants

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Hallucinogens

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CNS Stimulants and Cognitive Enhancers

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