Central Nervous System Pharmacology — MCQs

Central Nervous System Pharmacology Indian Medical PG Practice Questions and MCQs

Question 461: Which of the following is NOT an anti-craving agent for alcohol dependence?

A. Lorazepam (Correct Answer)
B. Acamprosate
C. Topiramate
D. Naltrexone

Explanation: ### Explanation The management of Alcohol Use Disorder is divided into two phases: **Management of Acute Withdrawal** and **Prevention of Relapse (Maintenance of Abstinence).** **1. Why Lorazepam is the correct answer:** Lorazepam is a **Benzodiazepine**. In alcohol dependence, benzodiazepines are the drugs of choice for managing **acute withdrawal symptoms** (like tremors, seizures, and delirium tremens) because they show cross-tolerance with alcohol and substitute for its GABAergic effects. However, they do **not** reduce the psychological "craving" for alcohol. In fact, due to their high addiction potential, they are generally avoided in long-term maintenance therapy. **2. Why the other options are incorrect:** * **Acamprosate:** An NMDA receptor antagonist and GABA-A agonist. It helps maintain abstinence by reducing the "negative reinforcement" (protracted withdrawal symptoms) and is a classic anti-craving agent. * **Naltrexone:** An opioid antagonist that blocks the μ-opioid receptors. It reduces the "rewarding" effects of alcohol (positive reinforcement), thereby decreasing the urge to drink. * **Topiramate:** An anti-epileptic that facilitates GABA neurotransmission and inhibits glutamate. It is used off-label as an effective agent to reduce alcohol cravings and heavy drinking days. **Clinical Pearls for NEET-PG:** * **Acamprosate** is the drug of choice for patients with **liver disease** (it is renally excreted). * **Naltrexone** is contraindicated in patients with acute hepatitis or liver failure and those on opioid painkillers. * **Disulfiram** is an "Aversion Therapy" agent (aldehyde dehydrogenase inhibitor), not primarily an anti-craving agent, as it works by causing unpleasant reactions if alcohol is consumed. * **Baclofen** is another emerging anti-craving agent, especially useful in patients with alcoholic liver disease.

Question 462: Perampanel is:

A. NMDA antagonist
B. AMPA antagonist (Correct Answer)
C. GABA mimetic
D. Calcium channel inhibitor

Explanation: **Explanation:** **Perampanel** is a first-in-class antiepileptic drug (AED) that acts as a **selective, non-competitive antagonist at the AMPA (α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid) receptor**. 1. **Why Option B is Correct:** Glutamate is the primary excitatory neurotransmitter in the brain. It acts on ionotropic receptors: NMDA, AMPA, and Kainate. AMPA receptors mediate the fast component of excitatory postsynaptic currents. By selectively blocking these receptors on postsynaptic neurons, Perampanel reduces neuronal over-excitation and prevents the spread of seizure activity. 2. **Why Other Options are Incorrect:** * **NMDA Antagonists (Option A):** Drugs like Ketamine, Memantine, and Felbamate act here. While Felbamate has NMDA antagonist properties, Perampanel is specific to AMPA. * **GABA Mimetics (Option C):** These enhance inhibitory neurotransmission. Examples include Benzodiazepines, Barbiturates, and Tiagabine. * **Calcium Channel Inhibitors (Option D):** Ethosuximide (T-type) and Gabapentin/Pregabalin (α2δ subunit of voltage-gated Ca²⁺ channels) work via this mechanism. **High-Yield Clinical Pearls for NEET-PG:** * **Indication:** Used for focal-onset seizures and primary generalized tonic-clonic seizures. * **Pharmacokinetics:** It has a very **long half-life** (~105 hours), allowing for once-daily dosing. * **Black Box Warning:** It is notorious for causing **serious neuropsychiatric events**, including aggression, hostility, irritability, and suicidal ideation. * **Metabolism:** It is metabolized by CYP3A4; therefore, enzyme-inducing AEDs (like Carbamazepine or Phenytoin) can significantly decrease its plasma concentration.

Question 463: A patient with Parkinsonism is managed with levodopa. What happens if Vitamin B complex is administered concurrently to the patient?

A. The action of levodopa in the brain will be potentiated.
B. Decarboxylation of levodopa in the brain will be decreased.
C. Side effects will be ameliorated.
D. Decreased efficacy will result. (Correct Answer)

Explanation: The correct answer is **D. Decreased efficacy will result.** **Mechanism of Interaction:** Levodopa is a precursor to dopamine that must cross the blood-brain barrier (BBB) to be effective. In the periphery, levodopa is converted to dopamine by the enzyme **Dopa decarboxylase (DDC)** [1]. Vitamin B6 (Pyridoxine), a common component of Vitamin B complex, acts as a **cofactor** for DDC. When administered concurrently, Pyridoxine accelerates the peripheral decarboxylation of levodopa into dopamine. Since dopamine cannot cross the BBB, less levodopa remains available to enter the brain, leading to a significant reduction in therapeutic efficacy [1]. **Analysis of Incorrect Options:** * **Option A:** The action is not potentiated; it is diminished because the drug is "wasted" in the systemic circulation before reaching its target site. * **Option B:** Decarboxylation in the brain is not the primary issue; rather, it is the **increased peripheral decarboxylation** that prevents the drug from reaching the brain. * **Option C:** Side effects are actually **increased**. Higher peripheral dopamine levels lead to greater activation of systemic receptors, causing nausea, vomiting, and cardiac arrhythmias. **NEET-PG High-Yield Pearls:** * **The Carbidopa Solution:** Modern formulations combine Levodopa with **Carbidopa** (a peripheral DDC inhibitor). Carbidopa does not cross the BBB, so it prevents peripheral conversion but allows central conversion [1]. * **Pyridoxine Paradox:** The interaction between Vitamin B6 and Levodopa **does not occur** if the patient is taking the Levodopa-Carbidopa combination, as Carbidopa effectively blocks the Pyridoxine-enhanced peripheral metabolism. * **Dietary Advice:** Patients on plain Levodopa should be advised to avoid high-protein meals (which compete for transport) and excessive Pyridoxine intake.

Question 464: Naltrexone is used for which of the following poisonings?

A. Heroin (Correct Answer)
B. Atropine
C. Cannabis
D. Diazepam

Explanation: **Explanation:** **Naltrexone** is a long-acting, competitive **opioid receptor antagonist**. It binds with high affinity to $\mu$-opioid receptors, effectively blocking the effects of exogenous opioids. 1. **Why Heroin is Correct:** Heroin is a semi-synthetic opioid that is metabolized to morphine. In the management of opioid use disorder, Naltrexone is used for **relapse prevention** (maintenance therapy) after detoxification. By blocking the "high" or euphoric effects of heroin, it helps extinguish the drug-seeking behavior. *Note: While Naloxone is used for acute overdose, Naltrexone is preferred for long-term abstinence due to its superior oral bioavailability and long half-life (up to 24–48 hours).* 2. **Why Other Options are Incorrect:** * **Atropine:** This is an anticholinergic drug. Poisoning is treated with **Physostigmine** (a cholinesterase inhibitor). * **Cannabis:** There is no specific pharmacological antagonist for cannabis; management is primarily supportive (e.g., benzodiazepines for agitation). * **Diazepam:** This is a benzodiazepine. The specific competitive antagonist used for benzodiazepine overdose is **Flumazenil**. **High-Yield Clinical Pearls for NEET-PG:** * **Naltrexone vs. Naloxone:** Remember "Nal**o**xone is for **O**verdose (Acute)" and "Naltrex**one** is for **One**-day-at-a-time (Maintenance)." * **Alcoholism:** Naltrexone is also FDA-approved for **Alcohol Dependence** as it reduces cravings by blocking endogenous opioid-mediated reward pathways. * **Contraindication:** Never administer Naltrexone to a patient currently dependent on opioids without detoxification, as it will precipitate **severe acute withdrawal syndrome**. * **Vivitrol:** This is the extended-release injectable form of Naltrexone given once monthly.

Question 465: Which of the following is not a new drug for Migraine?

A. Lasmiditan
B. Ubrogepant
C. Rimegepant
D. Romosozumab (Correct Answer)

Explanation: **Explanation:** The correct answer is **Romosozumab** because it is not used for migraine; it is a monoclonal antibody used to treat **severe osteoporosis** in postmenopausal women at high risk of fracture. It works by inhibiting **sclerostin**, thereby increasing bone formation and decreasing bone resorption. **Analysis of Incorrect Options:** * **Lasmiditan:** This is a first-in-class **5-HT1F receptor agonist**. Unlike triptans (5-HT1B/1D), it lacks vasoconstrictive properties, making it a safe alternative for migraine patients with cardiovascular contraindications. * **Ubrogepant & Rimegepant:** These belong to the **"Gepants"** class. they are small-molecule **CGRP (Calcitonin Gene-Related Peptide) receptor antagonists** approved for the acute treatment of migraine. Rimegepant is unique as it is approved for both acute treatment and prevention. **High-Yield Clinical Pearls for NEET-PG:** 1. **CGRP Pathway:** This is the most important recent target in migraine pharmacology. * *Monoclonal Antibodies (mAbs) for Prophylaxis:* Erenumab (targets CGRP receptor); Fremanezumab, Galcanezumab, and Eptinezumab (target CGRP ligand). * *Small Molecules (Gepants) for Acute/Prophylaxis:* Ubrogepant, Rimegepant, Atogepant. 2. **Lasmiditan Side Effect:** The most common side effect is **dizziness/somnolence**; patients are advised not to drive for 8 hours after intake. 3. **Romosozumab Warning:** It carries a boxed warning for increased risk of myocardial infarction, stroke, and cardiovascular death.

Question 466: Adverse effects of valproic acid include:

A. Alopecia
B. Fulminant hepatitis
C. Pancreatitis
D. All of the above (Correct Answer)

Explanation: **Explanation:** Valproic acid (Sodium Valproate) is a broad-spectrum antiepileptic drug that acts by multiple mechanisms, including blocking voltage-gated sodium channels, increasing GABA levels, and inhibiting T-type calcium channels. While highly effective, it is associated with a distinct profile of adverse effects. **Analysis of Options:** * **A. Alopecia:** Valproate frequently causes dose-related hair thinning or loss (alopecia). Interestingly, when the hair regrows, it may become curly. * **B. Fulminant Hepatitis:** This is a rare but life-threatening idiosyncratic reaction. It is most common in children under two years of age, especially those on polytherapy or with underlying metabolic disorders. Monitoring Liver Function Tests (LFTs) is mandatory. * **C. Pancreatitis:** Acute pancreatitis is a serious, potentially fatal side effect of valproate that can occur at any time during treatment, regardless of the dose or duration. Since all three conditions are documented adverse effects, **Option D (All of the above)** is the correct answer. **High-Yield Clinical Pearls for NEET-PG:** * **Mnemonic (VALPROATE):** **V**omiting, **A**lopecia, **L**iver toxicity, **P**ancreatitis/PCOS, **R**etention of weight (Obesity), **O**edema, **A**teratogenicity (Neural Tube Defects), **T**remors, **E**nzyme inhibitor. * **Teratogenicity:** It is the most teratogenic antiepileptic, specifically causing **Spina Bifida** (Neural Tube Defects). * **Metabolism:** Unlike many other antiepileptics (like Phenytoin or Carbamazepine), Valproate is a **Microsomal Enzyme Inhibitor**. * **Drug of Choice:** It remains the first-line treatment for Generalized Tonic-Clonic Seizures (GTCS), Myoclonic seizures, and Absence seizures.

Question 467: Which of the following is a cranial patch used in the management of Parkinson's disease?

A. Levodopa
B. Rotigotine (Correct Answer)
C. Apomorphine
D. Arantil

Explanation: Explanation: Rotigotine is the correct answer because it is a non-ergoline dopamine agonist (D3/D2/D1) uniquely formulated as a transdermal patch. In Parkinson’s disease, it provides continuous dopaminergic stimulation (CDS), which helps maintain stable plasma levels and reduces "off" periods compared to pulsatile oral dosing. Analysis of Options: * Levodopa (Option A): The gold standard for Parkinson’s, but it is administered orally (often with Carbidopa) [2], [5]. While intestinal gels (Duopa) exist for advanced stages, there is no transdermal patch formulation due to its chemical properties and high dosage requirements. * Apomorphine (Option B): A potent dopamine agonist used for "rescue" therapy in severe off-episodes [1]. It is administered via subcutaneous injection or continuous infusion pump, not a patch, due to extensive first-pass metabolism. * Arantil (Option D): This is a distractor and not a standard pharmacological treatment for Parkinson’s disease. High-Yield NEET-PG Clinical Pearls: * Rotigotine Patch: The most common side effect is application site reactions (erythema/itching). It should be rotated to a different site daily. * Dopamine Agonists: Divided into Ergot (Bromocriptine, Cabergoline—linked to cardiac valvular fibrosis) [4] and Non-Ergot (Pramipexole, Ropinirole, Rotigotine—preferred due to fewer side effects) [3]. * Impulse Control Disorders: All dopamine agonists (especially non-ergots) are associated with side effects like pathological gambling, hypersexuality, and binge eating [1], [4]. * Apomorphine: Always remember it is highly emetogenic; patients must be pre-treated with Trimethobenzamide (Domperidone is also used, but Ondansetron is contraindicated due to severe hypotension).

Question 468: Dextromethorphan differs from codeine in which of the following aspects?

A. Its antitussive action can be blocked by naloxone.
B. It depresses the mucociliary function of the airway mucosa.
C. Addiction is common.
D. It causes no constipation. (Correct Answer)

Explanation: **Explanation:** **Dextromethorphan** is the d-isomer of the codeine analogue levorphanol. While it is chemically related to opioids, its pharmacological profile differs significantly from traditional opioids like codeine. **Why Option D is Correct:** Unlike codeine, dextromethorphan does not act on peripheral μ-opioid receptors in the gastrointestinal tract. Therefore, it does not inhibit intestinal motility and **does not cause constipation**, which is a hallmark side effect of codeine. **Analysis of Incorrect Options:** * **Option A:** Dextromethorphan acts primarily on the cough center in the medulla via NMDA receptor antagonism and sigma-1 receptor stimulation, rather than traditional opioid receptors. Consequently, its antitussive effect is **not antagonized by naloxone**. * **Option B:** Codeine and other opioids can impair the clearance of secretions by depressing mucociliary activity. Dextromethorphan is preferred in clinical practice because it **does not depress mucociliary function**, allowing for better airway clearance. * **Option C:** Dextromethorphan lacks significant analgesic properties and does not produce euphoria at standard therapeutic doses. It has **low abuse potential**, and addiction is rare compared to codeine. **High-Yield NEET-PG Pearls:** * **Mechanism:** D-isomer of levorphanol; acts as an NMDA receptor antagonist. * **Toxicity:** In massive overdose, it can cause hallucinations and "dissociative" effects (similar to PCP/Ketamine). * **Drug Interaction:** It can precipitate **Serotonin Syndrome** if co-administered with SSRIs or MAO inhibitors, as it inhibits serotonin reuptake. * **Clinical Advantage:** It is the antitussive of choice when constipation or sedation must be avoided.

Question 469: All of the following act through GABAA receptors except?

A. Benzodiazepines
B. Barbiturates
C. Zopiclone
D. Promethazine (Correct Answer)

Explanation: **Explanation:** The question tests the knowledge of sedative-hypnotic mechanisms and neurotransmitter receptors. The **GABA-A receptor** is a ligand-gated chloride channel. When activated, it increases chloride influx, leading to hyperpolarization and CNS depression. **Why Promethazine is the correct answer:** Promethazine is a **first-generation H1-receptor antagonist** (antihistamine) with significant anticholinergic and alpha-adrenergic blocking properties. While it causes sedation as a side effect, its mechanism of action is the competitive blockade of histamine H1 receptors in the brain, **not** through the GABA-A receptor complex. **Why the other options are incorrect:** * **Benzodiazepines (e.g., Diazepam):** These act as positive allosteric modulators. They bind to a specific site on the GABA-A receptor and increase the **frequency** of chloride channel opening. * **Barbiturates (e.g., Phenobarbital):** These bind to a different site on the GABA-A receptor and increase the **duration** of chloride channel opening. At high doses, they can also act as GABA-mimetics. * **Zopiclone:** This belongs to the "Z-drugs" (Non-benzodiazepine hypnotics). Despite having a different chemical structure, Zopiclone binds to the **BZ1 (omega-1) subunit** of the GABA-A receptor to exert its hypnotic effect. **High-Yield Clinical Pearls for NEET-PG:** * **Flumazenil** is the specific antagonist for both Benzodiazepines and Z-drugs, but it does **not** reverse Barbiturate toxicity. * **Promethazine** is frequently used clinically for motion sickness and as an antiemetic due to its action on the chemoreceptor trigger zone (CTZ). * **GABA-B receptors** are G-protein coupled receptors (GPCRs); **Baclofen** is the classic agonist acting at this site.

Question 470: Side effects of diphenylhydantoin may include all except?

A. Gingival hyperplasia
B. Acute cerebellar syndrome
C. Inter-nuclear ophthalmoplegia (Correct Answer)
D. Megaloblastic anaemia

Explanation: **Explanation:** **Diphenylhydantoin (Phenytoin)** is a widely used hydantoin derivative for epilepsy. The correct answer is **Inter-nuclear ophthalmoplegia (INO)** because it is a localized brainstem lesion (typically involving the medial longitudinal fasciculus) most commonly associated with Multiple Sclerosis or strokes, not drug toxicity. **Why the other options are incorrect (Side effects of Phenytoin):** * **Gingival Hyperplasia:** A classic side effect occurring in ~20% of patients due to overgrowth of gum tissue (fibroblast proliferation). * **Acute Cerebellar Syndrome:** Phenytoin has a high affinity for the cerebellum. Toxicity manifests as **nystagmus**, ataxia, dysarthria, and diplopia. * **Megaloblastic Anaemia:** Phenytoin interferes with folate absorption and metabolism, leading to macrocytic anemia. **High-Yield Clinical Pearls for NEET-PG:** To remember the side effects of Phenytoin, use the mnemonic **"HOT MALAI"**: * **H** – Hirsutism, Hypertrophy of gums (Gingival hyperplasia) * **O** – Osteomalacia (due to Vitamin D metabolism interference) * **T** – Teratogenicity (**Fetal Hydantoin Syndrome**: cleft lip/palate, microcephaly) * **M** – Megaloblastic anemia * **A** – Ataxia (Cerebellar signs) * **L** – Lymphadenopathy (Pseudolymphoma) * **A** – Arrhythmias (when given as rapid IV bolus) * **I** – Insulin inhibition (leading to hyperglycemia) **Pharmacokinetics Note:** Phenytoin follows **Zero-order kinetics** (Capacity-limited metabolism) at therapeutic or high doses, meaning small dose increases can lead to disproportionate rises in plasma levels and toxicity.

Practice by Chapter

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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