Central Nervous System Pharmacology Practice Questions

Q: Which of the following is not an antiepileptic agent?

Flunarizine. **Explanation:** The correct answer is **Flunarizine**. While it is a pharmacological agent acting on the CNS, it is not classified as an antiepileptic drug (AED). **1. Why Flunarizine is the correct answer:** Flunarizine is a **non-selective calcium channel blocker** with additional dopamine D2 receptor blocking activity. Its primary clinical use is in the **prophylaxis of migraine** and the management of vertigo (vestibular disorders). Unlike AEDs, it does not stabilize neuronal membranes against high-frequency firing or enhance GABAergic inhibition to prevent seizures. **2. Why the other options are incorrect:** * **Phenytoin (Option A):** A classic first-generation AED. It works by blocking voltage-gated sodium channels in their inactive state, preventing the spread of seizure activity. * **Topiramate (Option C):** A broad-spectrum AED with multiple mechanisms: blocking sodium channels, enhancing GABA activity, and antagonizing AMPA/kainate glutamate receptors. It is used for both focal/generalized seizures and migraine prophylaxis. * **Carbamazepine (Option D):** An iminostilbene derivative and a first-line agent for focal seizures and trigeminal neuralgia. It works primarily by stabilizing inactivated sodium channels. **Clinical Pearls for NEET-PG:** * **Flunarizine Side Effects:** Can cause **extrapyramidal symptoms (EPS)** and depression due to its D2 blocking property; it is contraindicated in Parkinson’s disease. * **Drug of Choice (DOC):** * Trigeminal Neuralgia: Carbamazepine. * Absence Seizures: Ethosuximide (Valproate if generalized tonic-clonic seizures coexist). * Myoclonic Seizures: Valproate. * **Teratogenicity:** Phenytoin is associated with **Fetal Hydantoin Syndrome**, while Valproate is associated with **Neural Tube Defects**.

Q: Which of the following medications is used to maintain abstinence in alcohol dependence?

Naltrexone. **Explanation:** The management of alcohol dependence is divided into two phases: treatment of acute withdrawal and **maintenance of abstinence** (prevention of relapse). **Correct Option: A. Naltrexone** Naltrexone is an **opioid receptor antagonist** that is considered a first-line drug for maintaining abstinence. It works by blocking the $\mu$-opioid receptors, thereby reducing the "reward" or euphoria associated with alcohol consumption and significantly decreasing **craving**. Unlike disulfiram, it can be started while the patient is still drinking. **Incorrect Options:** * **B. Clonidine:** This is an $\alpha_2$-agonist used to manage the **autonomic hyperactivity** (tachycardia, hypertension) seen during *acute alcohol withdrawal*. It does not prevent relapse or maintain long-term abstinence. * **C. Disulfiram:** While used in alcohol dependence, it is an **aversion therapy** agent. It inhibits *aldehyde dehydrogenase*, causing a buildup of acetaldehyde if alcohol is consumed. However, recent clinical guidelines (and frequently NEET-PG patterns) prioritize Naltrexone and Acamprosate as superior for "maintaining abstinence" due to better compliance and reduced craving. * **D. Naloxone:** This is a short-acting opioid antagonist used intravenously for the emergency reversal of **acute opioid overdose**. It has no role in the long-term management of alcohol dependence due to its poor oral bioavailability and short half-life. **High-Yield Clinical Pearls for NEET-PG:** * **Acamprosate** (NMDA antagonist) is the other first-line drug for abstinence, especially useful in patients with liver disease (as Naltrexone is hepatotoxic). * **Disulfiram** does NOT reduce craving; it only acts as a psychological deterrent. * **Benzodiazepines** (e.g., Chlordiazepoxide) remain the "Gold Standard" for managing **acute withdrawal symptoms** and preventing seizures/delirium tremens.

Q: What is a known side effect of Levodopa?

On-off phenomenon. **Explanation:** **Levodopa** is the metabolic precursor of dopamine and remains the gold standard for managing Parkinson’s disease. The **"On-off phenomenon"** is a classic long-term complication of Levodopa therapy, typically occurring after 3–5 years of treatment. 1. **Why Option D is Correct:** The "On-off phenomenon" refers to sudden, unpredictable fluctuations in motor performance. The "On" period represents improved mobility (often accompanied by dyskinesias), while the "Off" period involves a sudden return of severe parkinsonian symptoms. This occurs due to the progressive loss of dopaminergic neurons, which reduces the brain's capacity to store dopamine, making the patient's clinical state entirely dependent on the fluctuating plasma levels of the drug. 2. **Why Other Options are Incorrect:** * **A. Spasticity:** This is a feature of Upper Motor Neuron (UMN) lesions. Parkinson’s is an extrapyramidal disorder characterized by **rigidity** (lead-pipe or cogwheel), not spasticity. * **B. Tremor:** Resting tremor is a primary symptom of Parkinson’s disease itself. Levodopa is used to *treat* tremors, not cause them. * **C. Akinesia:** Similar to tremor, akinesia (poverty of movement) is a cardinal symptom of the disease that Levodopa aims to alleviate. **High-Yield NEET-PG Pearls:** * **Peripheral Decarboxylase Inhibitors (Carbidopa/Benserazide):** Always co-administered with Levodopa to prevent peripheral conversion to dopamine, thereby reducing systemic side effects like nausea, vomiting, and cardiac arrhythmias. * **Vitamin B6 (Pyridoxine):** It is a cofactor for DOPA decarboxylase; taking it with Levodopa (without Carbidopa) enhances peripheral metabolism, reducing the drug's efficacy. * **Adverse Effects:** Early effects include GI distress and postural hypotension; late effects include dyskinesias and psychosis.

Q: What is the drug of choice for rapid cyclers in manic-depressive psychosis?

Valproate. **Explanation:** **Valproate** is the drug of choice for **rapid cyclers** (defined as ≥4 episodes of mania or depression per year) and **mixed episodes** in Bipolar Affective Disorder (BPAD). While Lithium remains the gold standard for classic bipolar disorder, it is notably less effective in patients with rapid cycling patterns. Valproate’s superior efficacy in these cases is attributed to its multi-modal mechanism, including GABA enhancement and modulation of glutamate and sodium channels. **Analysis of Options:** * **Valproate (Correct):** Preferred for rapid cycling, mixed states, and patients who do not respond to Lithium. * **Lithium (Incorrect):** Though the first-line agent for typical mania and prophylaxis, it has a high failure rate in rapid cyclers. * **Carbamazepine (Incorrect):** Used as a second-line mood stabilizer or in refractory cases, but it is not the primary drug of choice for rapid cycling. It is also a potent enzyme inducer, complicating its side-effect profile. * **Phenytoin (Incorrect):** This is an anti-epileptic drug with no established role as a mood stabilizer in psychiatric practice. **High-Yield Clinical Pearls for NEET-PG:** * **Therapeutic Window:** Lithium has a narrow therapeutic index (0.8–1.2 mEq/L for acute mania; 0.5–0.8 mEq/L for maintenance). * **Teratogenicity:** Lithium causes **Ebstein’s Anomaly** (tricuspid valve defect), while Valproate is associated with **Neural Tube Defects** (Spina Bifida). * **Drug of Choice Summary:** * Classic Mania: Lithium * Rapid Cyclers/Mixed Mania: Valproate * Bipolar Depression: Quetiapine, Lurasidone, or Lamotrigine.

Q: Which of the following compounds acts as a benzodiazepine antagonist?

Flumazenil. **Explanation:** **Correct Option: A. Flumazenil** Flumazenil is a specific **competitive antagonist** at the benzodiazepine (BZD) binding site on the **GABA-A receptor** complex [1], [2]. It blocks the actions of benzodiazepines and "Z-drugs" (Zolpidem, Zopiclone) but does not affect the actions of barbiturates or alcohol, as they bind to different sites [2], [3]. It is primarily used to reverse BZD-induced sedation for anesthesia or in the management of benzodiazepine overdose [2]. **Incorrect Options:** * **B. Naloxone:** This is a competitive **opioid antagonist** used for the emergency reversal of opioid overdose (e.g., morphine, heroin). It has no effect on GABA receptors. * **C. Furazolidone:** This is a nitrofuran derivative with **antibacterial and antiprotozoal** properties, commonly used for infectious diarrhea and giardiasis. It also possesses mild MAO-inhibitory activity. * **D. Naltrexone:** This is a long-acting **opioid antagonist**. While Naloxone is used for acute reversal, Naltrexone is used for the long-term maintenance of opioid-free states and to reduce cravings in alcohol dependence. **High-Yield Clinical Pearls for NEET-PG:** * **Half-life:** Flumazenil has a very short half-life (~1 hour). Because many benzodiazepines (like Diazepam) have longer half-lives, **re-sedation** can occur, requiring repeated doses or an infusion. * **Seizure Risk:** The most serious side effect of Flumazenil is the induction of **seizures**, especially in patients with long-term BZD dependence or those who have co-ingested tricyclic antidepressants (TCAs) [1]. * **Inverse Agonist:** Do not confuse Flumazenil (antagonist) with **Beta-carbolines**, which act as inverse agonists at the BZD site and can cause convulsions [1].

Q: Which of the following represents the mechanism of action of Memantine?

NMDA antagonist. **Explanation:** **1. Why the Correct Answer is Right (NMDA Antagonist):** Memantine is a low-to-moderate affinity, non-competitive **NMDA (N-methyl-D-aspartate) receptor antagonist**. In Alzheimer’s disease, chronic overstimulation of NMDA receptors by glutamate leads to excessive calcium influx into neurons, causing "excitotoxicity" and neuronal death. Memantine blocks these receptors under conditions of excessive stimulation but allows for normal physiological signaling required for memory formation. It is specifically FDA-approved for **moderate-to-severe Alzheimer’s disease**. **2. Why the Incorrect Options are Wrong:** * **GABA antagonist (A):** GABA is the primary inhibitory neurotransmitter. Antagonizing it would lead to CNS excitation and seizures (e.g., Picrotoxin), which is the opposite of the desired effect in neurodegenerative management. * **Alpha 2 antagonist (B):** These drugs (e.g., Yohimbine, Mirtazapine) increase sympathetic outflow or serotonin/norepinephrine release. They are used in treating depression or erectile dysfunction, not dementia. * **5HT 2A antagonist (C):** This is the mechanism of atypical antipsychotics (e.g., Risperidone) and certain antidepressants (e.g., Trazodone). While used to manage behavioral symptoms in dementia, it is not the mechanism of Memantine. **3. Clinical Pearls for NEET-PG:** * **Combination Therapy:** Memantine is often combined with Donepezil (an AChE inhibitor) for synergistic effects in advanced Alzheimer's. * **Side Effects:** Generally well-tolerated; the most common side effects are **dizziness, headache, and confusion**. * **Excretion:** It is primarily excreted unchanged by the kidneys; dose adjustment is required in renal impairment. * **Key Distinction:** Unlike Donepezil (used for mild-to-moderate cases), Memantine is the drug of choice for **moderate-to-severe** Alzheimer's.

Q: Which of the following opioids is 100 times more potent than morphine?

Fentanyl. **Explanation:** **Correct Option: B (Fentanyl)** Fentanyl is a synthetic opioid agonist that acts primarily on the $\mu$ (mu) receptors. It is highly lipophilic, allowing it to cross the blood-brain barrier rapidly. In clinical practice, Fentanyl is approximately **100 times more potent than Morphine**. This high potency is due to its high affinity for the $\mu$-receptor and its rapid onset of action. It is commonly used in anesthesia (induction and maintenance) and for chronic pain management via transdermal patches. **Incorrect Options:** * **A & D (Pethidine/Meperidine):** These are the same drug. Pethidine is significantly **less potent** than morphine (roughly 1/10th the potency). It is unique because it has anticholinergic properties (causing tachycardia) and its metabolite, *normeperidine*, can cause seizures in patients with renal failure. * **C (Pentazocine):** This is an opioid agonist-antagonist ( $\kappa$-agonist and weak $\mu$-antagonist/partial agonist). It is much less potent than morphine and can precipitate withdrawal symptoms in opioid-dependent individuals. **High-Yield NEET-PG Pearls:** * **Potency Hierarchy:** Sufentanil (1000x) > Remifentanil/Fentanyl (100x) > Morphine (1x) > Pethidine (0.1x). * **Sufentanil** is the most potent opioid used clinically (500–1000 times more potent than morphine). * **Remifentanil** is notable for its ultra-short duration of action due to metabolism by plasma and tissue esterases. * **Miosis** is a classic sign of opioid overdose, but **Pethidine** is an exception (it may cause mydriasis due to its atropine-like action).

Question 1

Which statement is true regarding morphine?

Accepted Answer

Tolerance develops for all effects except miosis and constipation.

Answer

Tolerance to all effects develops with chronic usage.

Answer

Tolerance develops for all effects except euphoria and sedation.

Answer

Tolerance can develop to all effects in high doses.

Question 2

Which of the following is not an antiepileptic agent?

Accepted Answer

Flunarizine

Answer

Phenytoin

Answer

Topiramate

Answer

Carbamazepine

Question 3

Which of the following medications is used to maintain abstinence in alcohol dependence?

Accepted Answer

Naltrexone

Answer

Clonidine

Answer

Disulfiram

Answer

Naloxone

Question 4

Which of the following adverse effects of levodopa is not minimized even after combining it with carbidopa?

Accepted Answer

Involuntary movements

Answer

Nausea and vomiting

Answer

Cardiac arrhythmia

Answer

'On-off' effect

Question 5

What is a known side effect of Levodopa?

Accepted Answer

On-off phenomenon

Answer

Spasticity

Answer

Tremor

Answer

Akinesia

Question 6

What is the drug of choice for rapid cyclers in manic-depressive psychosis?

Accepted Answer

Valproate

Answer

Carbamazepine

Answer

Phenytoin

Answer

Lithium

Question 7

Which of the following compounds acts as a benzodiazepine antagonist?

Accepted Answer

Flumazenil

Answer

Naloxone

Answer

Furazolidone

Answer

Naltrexone

Question 8

All of the following are true about Clozapine except?

Accepted Answer

Blood level below 350 ng/ml should be maintained to avoid agranulocytosis.

Answer

More potently blocks D2 as compared to D1 receptors.

Answer

Should not be used along with Carbamazepine.

Answer

Should be discontinued if the WBC count is below 3,000/mm³ cells.

Question 9

Which of the following represents the mechanism of action of Memantine?

Accepted Answer

NMDA antagonist

Answer

GABA antagonist

Answer

Alpha 2 antagonist

Answer

5HT 2A antagonist

Question 10

Which of the following opioids is 100 times more potent than morphine?

Accepted Answer

Fentanyl

Answer

Pethidine

Answer

Pentazocine

Answer

Meperidine

Central Nervous System Pharmacology — MCQs

Central Nervous System Pharmacology — MCQs

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