Central Nervous System Pharmacology — MCQs

Central Nervous System Pharmacology Indian Medical PG Practice Questions and MCQs

Question 141: All of the following drugs are used for migraine prophylaxis except?

A. Propranolol
B. Topiramate
C. Flunarizine
D. None of the above (Correct Answer)

Explanation: The correct answer is **None of the above** because all three listed drugs—Propranolol, Topiramate, and Flunarizine—are established first-line agents for the prophylaxis of migraine. ### **Explanation of Options:** * **Propranolol (Option A):** A non-selective beta-blocker and the **gold standard** for migraine prophylaxis. It works by modulating thalamocortical excitability and inhibiting vasodilation. It is the drug of choice unless contraindicated (e.g., in asthma or heart block). * **Topiramate (Option B):** An antiepileptic drug that is highly effective for migraine prevention. It acts by blocking voltage-gated sodium channels, enhancing GABA-A activity, and antagonizing glutamate receptors. It is particularly useful in patients with comorbid obesity as it causes weight loss. * **Flunarizine (Option C):** A non-selective calcium channel blocker with additional H1-blocking properties. It is widely used for prophylaxis, especially in patients who do not tolerate beta-blockers, though it may cause side effects like weight gain and sedation. ### **NEET-PG High-Yield Pearls:** * **Prophylaxis Criteria:** Indicated if the patient has >2-3 attacks per month, attacks are severe/disabling, or acute treatment is contraindicated. * **Drug of Choice (DOC):** Propranolol is generally considered the DOC for prophylaxis. * **Other Prophylactic Agents:** Amitriptyline (TCA), Valproate (Antiepileptic), and newer **CGRP Antagonists** (e.g., Erenumab). * **Acute Attack Treatment:** Triptans (5-HT 1B/1D agonists) are the DOC for moderate-to-severe acute migraine. * **Contraindication Tip:** Avoid Propranolol in asthmatics and Topiramate in patients with a history of nephrolithiasis (kidney stones).

Question 142: What is the drug of choice for trigeminal neuralgia?

A. Chlorpromazine
B. Carbamazepine (Correct Answer)
C. Gabapentin
D. Fluoxetine

Explanation: **Explanation:** **Carbamazepine** is the gold-standard **Drug of Choice (DOC)** for Trigeminal Neuralgia (Tic Douloureux). Trigeminal neuralgia is characterized by sudden, severe, lancinating facial pain. Carbamazepine works by blocking **use-dependent voltage-gated sodium channels**, which stabilizes neuronal membranes and inhibits the repetitive firing of the trigeminal nerve. **Analysis of Options:** * **Carbamazepine (Correct):** It is the first-line treatment due to its high efficacy in reducing the frequency and intensity of painful paroxysms. * **Chlorpromazine:** This is a typical antipsychotic (neuroleptic) used primarily in schizophrenia and for intractable hiccups; it has no role in managing neuropathic pain. * **Gabapentin:** While used for various neuropathic pains (like Post-Herpetic Neuralgia), it is considered a second-line agent for trigeminal neuralgia, usually reserved for patients who do not tolerate or respond to carbamazepine. * **Fluoxetine:** An SSRI antidepressant used for depression and OCD; it is not effective for the acute, stabbing pain of trigeminal neuralgia. **High-Yield Clinical Pearls for NEET-PG:** 1. **Mechanism:** Carbamazepine is an enzyme inducer (CYP3A4), leading to auto-induction of its own metabolism. 2. **Adverse Effects:** It can cause **diplopia, ataxia**, and serious dermatological reactions like **Stevens-Johnson Syndrome** (strongly associated with the **HLA-B*1502** allele in Asian populations). 3. **Monitoring:** Chronic use requires monitoring for **agranulocytosis** and **hyponatremia** (SIADH-like effect). 4. **Second-line agents:** Oxcarbazepine (better tolerated), Baclofen, and Lamotrigine. 5. **Surgical DOC:** Microvascular decompression (Janetta procedure).

Question 143: What is a recently approved drug for migraine prophylaxis?

A. Sumatriptan
B. Topiramate (Correct Answer)
C. Gabapentin
D. Propranolol

Explanation: **Explanation:** **Correct Answer: B. Topiramate** Topiramate is an antiepileptic drug that has become a mainstay for **migraine prophylaxis**. Its mechanism involves blocking voltage-gated sodium channels, augmenting GABA-A receptors, and antagonizing glutamate (AMPA/kainate) receptors. It is particularly favored because it helps in weight reduction (unlike valproate) and is highly effective in reducing the frequency of migraine attacks. While "recently approved" in the context of historical MCQ patterns refers to its transition from an anticonvulsant to a first-line prophylactic agent, it remains a high-yield "correct" choice in exams comparing it to older traditional therapies. **Analysis of Incorrect Options:** * **A. Sumatriptan:** This is a 5-HT$_{1B/1D}$ receptor agonist used for the **acute treatment** (abortive therapy) of migraine attacks, not for prophylaxis. * **C. Gabapentin:** While used off-label for various neuropathic pain syndromes, it is not considered a first-line agent for migraine prophylaxis and lacks the robust clinical evidence seen with Topiramate. * **D. Propranolol:** This is a non-selective beta-blocker and a classic first-line drug for migraine prophylaxis. However, it is an "older" drug compared to the newer antiepileptic approaches like Topiramate. **High-Yield Clinical Pearls for NEET-PG:** * **First-line Prophylactic Agents:** Beta-blockers (Propranolol), Anticonvulsants (Topiramate, Valproate), and TCAs (Amitriptyline). * **Side Effect Profile:** Topiramate is associated with **paresthesia, cognitive slowing ("dope-a-mate"), and nephrolithiasis** (kidney stones). * **Teratogenicity:** Topiramate is associated with an increased risk of **cleft lip/palate**; Valproate is associated with neural tube defects. * **Newest Class (Monoclonal Antibodies):** For the most recent updates, look for **CGRP antagonists** (e.g., Erenumab, Galcanezumab) which are the actual "latest" approved prophylactic drugs.

Question 144: Which of the following drugs are used in the treatment of ADHD?

A. Amphetamine
B. Modafinil
C. Methylphenidate
D. All the above (Correct Answer)

Explanation: **Explanation** Attention-Deficit Hyperactivity Disorder (ADHD) is characterized by a deficiency in catecholaminergic transmission (dopamine and norepinephrine) in the prefrontal cortex. Treatment aims to increase these neurotransmitter levels to improve focus and impulse control. * **Methylphenidate (Option C):** This is the **first-line drug of choice** for ADHD. It acts by blocking the reuptake of dopamine and norepinephrine (NDRI), thereby increasing their availability in the synaptic cleft. * **Amphetamines (Option A):** These are potent CNS stimulants that not only block reuptake but also promote the release of stored catecholamines from presynaptic vesicles. They are highly effective and widely used as first-line or second-line agents. * **Modafinil (Option B):** While primarily the drug of choice for **Narcolepsy**, Modafinil is used **off-label** in the management of ADHD, particularly in adults or when conventional stimulants are poorly tolerated. It promotes wakefulness and alertness with a lower risk of peripheral side effects compared to amphetamines. Since all three drugs are utilized in the clinical management of ADHD, **Option D (All the above)** is the correct answer. **High-Yield NEET-PG Pearls:** * **Non-Stimulant of Choice:** **Atomoxetine** (a selective Norepinephrine Reuptake Inhibitor) is preferred if there is a history of substance abuse, as it has no addiction potential. * **Side Effects:** Common side effects of stimulants include insomnia, decreased appetite, and **growth suppression** in children (requires "drug holidays"). * **Other Drugs:** Alpha-2 agonists like **Clonidine** and **Guanfacine** are used as adjuncts to manage impulsivity and aggression.

Question 145: All of the following drugs are used for managing status epilepticus except?

A. Phenytoin
B. Diazepam
C. Thiopentone sodium
D. Carbamazepine (Correct Answer)

Explanation: ### Explanation **Status Epilepticus (SE)** is a medical emergency defined as continuous seizure activity lasting more than 5 minutes or recurrent seizures without recovery of consciousness. Management requires **rapid-acting, intravenous (IV) medications** to terminate electrical activity immediately. #### Why Carbamazepine is the Correct Answer: **Carbamazepine** is contraindicated in the management of status epilepticus for two primary reasons: 1. **Formulation:** It is not available in an intravenous (IV) preparation; it is administered orally, making it too slow for emergency use. 2. **Paradoxical Effect:** In certain types of status (like absence or myoclonic status), carbamazepine can actually worsen the seizures. It is primarily used for long-term maintenance therapy of focal and generalized tonic-clonic seizures. #### Analysis of Other Options: * **Diazepam (Option B):** A Benzodiazepine (BZD). BZDs are the **first-line drugs** for terminating seizures due to their rapid onset of action via GABA-A receptor modulation. * **Phenytoin (Option A):** Used as a **second-line agent** (usually as Fosphenytoin) to prevent the recurrence of seizures after the initial bolus of a BZD. It provides longer-term stabilization. * **Thiopentone Sodium (Option C):** An ultra-short-acting barbiturate used in **refractory status epilepticus** (when first and second-line drugs fail). It requires ICU monitoring and intubation. #### NEET-PG High-Yield Pearls: * **Drug of Choice (DOC) for SE:** **Lorazepam (IV)** is preferred over Diazepam due to its longer duration of action in the brain. * **Fosphenytoin vs. Phenytoin:** Fosphenytoin is preferred because it is water-soluble, causes less local irritation (less risk of "Purple Glove Syndrome"), and can be infused faster. * **Refractory SE:** Defined as failure of BZD + one second-line agent. Drugs used include **Propofol, Midazolam infusion, or Thiopentone.** * **Carbamazepine Side Effect:** Watch for **SIADH (Hyponatremia)** and **Stevens-Johnson Syndrome** (associated with HLA-B*1502).

Question 146: Which of the following is a long-acting full agonist oral opiate used for heroin detoxification or long-term maintenance?

A. Morphine
B. Fentanyl
C. Methadone (Correct Answer)
D. None of the above

Explanation: **Explanation:** **Methadone** is the gold standard for the pharmacological management of opioid use disorder (heroin detoxification and maintenance). Its efficacy lies in its unique pharmacokinetic profile: it is a **synthetic full μ-opioid receptor agonist** with high oral bioavailability and an exceptionally **long half-life (24–52 hours)**. In detoxification, methadone prevents withdrawal symptoms by maintaining stable plasma levels, avoiding the "highs and lows" associated with shorter-acting opioids. In long-term maintenance, it induces cross-tolerance, which "blocks" the euphoric effects of illicit heroin if the patient relapses. **Analysis of Incorrect Options:** * **Morphine:** While a full agonist, it has a relatively short half-life (2–4 hours) and significant first-pass metabolism, making it unsuitable for stable long-term maintenance or preventing withdrawal over a 24-hour period. * **Fentanyl:** It is a highly potent, short-acting synthetic opioid. Due to its rapid onset and short duration of action, it is used for anesthesia and acute pain management, but it would worsen addiction cycles if used for detoxification. **High-Yield NEET-PG Pearls:** * **Mechanism:** Apart from being a μ-agonist, Methadone also acts as an **NMDA receptor antagonist**, which may help in reducing opioid tolerance and managing neuropathic pain. * **Side Effects:** A critical ECG finding associated with Methadone is **QTc interval prolongation**, which can lead to Torsades de Pointes. * **Metabolism:** It is primarily metabolized by **CYP3A4**; inhibitors of this enzyme can increase methadone levels, risking respiratory depression. * **Alternative:** **Buprenorphine** (a partial agonist) is also used for maintenance but has a "ceiling effect" on respiratory depression, making it safer in overdose.

Question 147: Sibutramine is indicated for which condition?

A. Smoking cessation
B. Obesity (Correct Answer)
C. Severe weight loss
D. Mania

Explanation: **Explanation:** **Sibutramine** is a centrally acting drug used in the management of **Obesity**. It acts as a **Serotonin and Norepinephrine Reuptake Inhibitor (SNRI)**. By inhibiting the reuptake of these neurotransmitters in the hypothalamus, it enhances satiety (feeling of fullness) and increases metabolic rate (thermogenesis), thereby facilitating weight loss. **Analysis of Options:** * **Option B (Obesity):** Correct. It was traditionally used as an adjunct to diet and exercise for weight loss in patients with a high BMI. * **Option A (Smoking cessation):** Incorrect. Drugs used for this purpose include **Varenicline** (partial agonist at α4β2 nicotinic receptors) and **Bupropion** (NDRI). * **Option C (Severe weight loss):** Incorrect. Sibutramine causes weight loss, not gain. For weight gain/appetite stimulation, drugs like **Megestrol acetate** or **Dronabinol** are used. * **Option D (Mania):** Incorrect. Sibutramine can actually precipitate mania or anxiety due to its sympathomimetic effects. Mania is treated with mood stabilizers like **Lithium** or **Valproate**. **High-Yield Clinical Pearls for NEET-PG:** * **Withdrawal:** Sibutramine was withdrawn from the market in many countries (including India and the USA) because the **SCOUT trial** showed an increased risk of **major adverse cardiovascular events (MACE)**, such as non-fatal MI and stroke. * **Contraindications:** It should be avoided in patients with a history of coronary artery disease, hypertension, or arrhythmias. * **Other Anti-obesity drugs:** * **Orlistat:** Gastric and pancreatic lipase inhibitor (causes steatorrhea). * **Lorcaserin:** 5-HT2C agonist (withdrawn due to cancer risk). * **Liraglutide:** GLP-1 receptor agonist. * **Phentermine + Topiramate:** Combination therapy.

Question 148: What is the mechanism of action of Tolcapone?

A. Dopa decarboxylase inhibitor
B. COMT inhibitor (Correct Answer)
C. MAO - A inhibitor
D. MAO - B inhibitor

Explanation: **Explanation:** **Mechanism of Action:** Tolcapone is a potent, reversible inhibitor of the enzyme **Catechol-O-methyltransferase (COMT)**. In the management of Parkinson’s disease, when Levodopa is administered, it is peripheralized by COMT into 3-O-methyldopa. Tolcapone inhibits this process, thereby increasing the bioavailability of Levodopa and extending its half-life. Unlike Entacapone (which acts only peripherally), **Tolcapone acts both peripherally and centrally**, crossing the blood-brain barrier to inhibit central COMT. **Analysis of Incorrect Options:** * **Option A (Dopa decarboxylase inhibitor):** This describes **Carbidopa** and **Benserazide**. These drugs prevent the peripheral conversion of Levodopa to Dopamine but do not affect the COMT pathway. * **Option C (MAO-A inhibitor):** These (e.g., **Moclobemide**) are primarily used as antidepressants. Inhibiting MAO-A in the presence of tyramine-rich foods can lead to a "cheese reaction." * **Option D (MAO-B inhibitor):** This describes **Selegiline** and **Rasagiline**. While these are used in Parkinson’s, they work by inhibiting the central breakdown of dopamine rather than the COMT-mediated metabolism of Levodopa. **High-Yield Clinical Pearls for NEET-PG:** * **The "Wearing-Off" Effect:** COMT inhibitors are specifically used to reduce "off" time in patients experiencing fluctuations in Levodopa response. * **Hepatotoxicity:** Tolcapone is associated with a risk of **fulminant hepatic failure**. Therefore, it requires regular liver function test (LFT) monitoring and is generally reserved for patients who do not respond to Entacapone. * **Discoloration:** A common side effect of COMT inhibitors is the harmless **orange discoloration of urine**.

Question 149: Which of the following medications is not used for alcohol detoxification?

A. Disulfiram
B. Flumazenil (Correct Answer)
C. Acamprosate
D. Naltrexone

Explanation: **Explanation:** The correct answer is **Flumazenil**. To answer this question correctly, it is essential to distinguish between drugs used for **alcohol withdrawal/detoxification** and those used for **relapse prevention (maintenance of abstinence)**. 1. **Why Flumazenil is the correct answer:** Flumazenil is a competitive **GABA-A receptor antagonist**. It is specifically used for the reversal of benzodiazepine overdose. It has no established role in the management of alcohol detoxification or dependence. In fact, using Flumazenil in a patient with chronic alcohol use can lower the seizure threshold, potentially precipitating withdrawal seizures. 2. **Why the other options are used in Alcohol Use Disorder:** * **Disulfiram:** An aldehyde dehydrogenase inhibitor. It causes the accumulation of acetaldehyde, leading to a highly unpleasant "disulfiram-like reaction" (nausea, flushing, tachycardia) if alcohol is consumed. It is used as **aversion therapy** for relapse prevention. * **Acamprosate:** A weak NMDA receptor antagonist and GABA-A activator. It helps reduce "protracted withdrawal" symptoms (insomnia, anxiety) and is used to maintain abstinence. * **Naltrexone:** An opioid receptor antagonist that reduces the "reward" or "high" associated with drinking by blocking endogenous opioid pathways. It reduces cravings and the risk of heavy drinking. **High-Yield NEET-PG Pearls:** * **Drug of Choice (DOC) for Alcohol Withdrawal:** Benzodiazepines (e.g., Chlordiazepoxide, Diazepam). * **DOC for Withdrawal in Liver Failure:** Lorazepam, Oxazepam, Temazepam (mnemonic: **LOT**—these bypass phase I hepatic metabolism). * **Wernicke’s Encephalopathy:** Always give **Thiamine** before Glucose to prevent precipitating acute neurological deterioration.

Question 150: What is the drug of choice for juvenile myoclonic epilepsy?

A. Phenytoin
B. Lamotrigine
C. Valproate (Correct Answer)
D. Zonisamide

Explanation: **Explanation:** **Juvenile Myoclonic Epilepsy (JME)**, also known as Janz syndrome, is a common idiopathic generalized epilepsy characterized by myoclonic jerks (typically in the morning), generalized tonic-clonic seizures (GTCS), and occasionally absence seizures. **Why Valproate is the Correct Answer:** Sodium Valproate is the **drug of choice** for JME because it is a broad-spectrum antiepileptic drug (AED) that effectively controls all three seizure types associated with the syndrome. It works by multiple mechanisms: blocking voltage-gated sodium channels, increasing GABA levels, and inhibiting T-type calcium channels. In JME, Valproate provides a high rate of seizure freedom (up to 80-90%), though it is often required lifelong as relapse rates are high upon discontinuation. **Analysis of Incorrect Options:** * **Phenytoin:** This is a narrow-spectrum AED. It is contraindicated in JME because it can **exacerbate** myoclonic jerks and absence seizures. * **Lamotrigine:** While effective for GTCS, Lamotrigine can sometimes worsen myoclonic seizures in JME patients. It is generally considered a second-line agent or an alternative in females of childbearing age. * **Zonisamide:** This is a broad-spectrum agent that may be used as an adjunct, but it is not the first-line gold standard compared to Valproate. **Clinical Pearls for NEET-PG:** * **Teratogenicity:** While Valproate is the most effective, it is highly teratogenic (Neural Tube Defects). In **females of childbearing age**, Levetiracetam or Lamotrigine are preferred alternatives. * **EEG Finding:** JME typically shows characteristic **4-6 Hz polyspike-and-wave** discharges. * **Avoidance:** Drugs that block sodium channels exclusively (Phenytoin, Carbamazepine, Oxcarbazepine) should be avoided in JME as they aggravate myoclonus.

Practice by Chapter

General Anesthetics

Practice Questions

Local Anesthetics

Practice Questions

Sedative-Hypnotics

Practice Questions

Antiepileptic Drugs

Practice Questions

Antiparkinsonian Drugs

Practice Questions

Opioid Analgesics

Practice Questions

Drugs of Abuse and Addiction

Practice Questions

Psychostimulants

Practice Questions

Hallucinogens

Practice Questions

CNS Stimulants and Cognitive Enhancers

Practice Questions

Want unlimited practice?

Get full access to all questions, explanations, and performance tracking.

Start For Free