Central Nervous System Pharmacology Practice Questions

Q: Phenytoin is most widely used for which of the following conditions?

All of the above. **Explanation:** Phenytoin is a versatile hydantoin derivative that acts primarily by blocking **voltage-gated sodium channels** in their inactivated state. This stabilizes neuronal membranes and prevents the high-frequency repetitive firing of action potentials, making it effective across several neurological conditions. * **Grand mal epilepsy (Generalized Tonic-Clonic Seizures):** Phenytoin is a first-line traditional drug for GTCS. It inhibits the spread of seizure activity without causing significant sedation. * **Status Epilepticus:** Intravenous (IV) phenytoin (or its prodrug, **Fosphenytoin**) is a standard second-line treatment used to prevent the recurrence of seizures after the acute episode has been controlled by benzodiazepines (like Lorazepam). * **Trigeminal Neuralgia:** While Carbamazepine is the drug of choice, Phenytoin is an effective alternative for patients who do not tolerate Carbamazepine or fail to respond to it. It works by reducing the paroxysmal discharges in the trigeminal nerve. **High-Yield NEET-PG Pearls:** 1. **Kinetics:** Phenytoin follows **Zero-order kinetics** (capacity-limited elimination) at therapeutic or high doses, meaning small dose increases can lead to disproportionate rises in plasma levels (toxicity). 2. **Side Effects (Mnemonic: HOT MALARIA):** **H**irsutism, **O**steomalacia, **T**eratogenicity (Fetal Hydantoin Syndrome), **M**egaloblastic anemia (folate deficiency), **A**taxia, **L**ymphadenopathy, **I**nsulin inhibition (hyperglycemia), **R**igidity, and **A**rrhythmias (when given rapid IV). 3. **Gingival Hyperplasia:** A classic side effect caused by overgrowth of gum tissue due to increased platelet-derived growth factor (PDGF). 4. **Fosphenytoin:** Preferred over Phenytoin for IV use as it is water-soluble, has a neutral pH, and does not cause "Purple Glove Syndrome."

Q: What is the new drug approved for the treatment of tardive dyskinesia?

Valbenazine. **Explanation:** **Valbenazine** is the first drug specifically FDA-approved for the treatment of **Tardive Dyskinesia (TD)**. TD is a movement disorder caused by long-term use of dopamine receptor blockers (antipsychotics), characterized by upregulation of dopamine receptors. Valbenazine acts as a highly selective **Vesicular Monoamine Transporter 2 (VMAT2) inhibitor**. By inhibiting VMAT2, it prevents the packaging of dopamine into presynaptic vesicles, thereby reducing dopamine release into the synaptic cleft and alleviating the hyperkinetic movements of TD. **Analysis of Options:** * **Safinamide (Option A):** This is a reversible MAO-B inhibitor used as an add-on treatment for Parkinson’s disease to manage "off" episodes. It has no role in treating TD. * **Tetrabenazine (Option B):** While it is a VMAT2 inhibitor used for Huntington’s Chorea, it is not specifically preferred for TD due to its short half-life and significant side effects like depression and parkinsonism. * **Deutetrabenazine (Option D):** This is a deuterated form of tetrabenazine. While it is also approved for TD, **Valbenazine** is often highlighted in exams as the "first" or "novel" specific agent with a superior pharmacokinetic profile (once-daily dosing and less risk of depression). **High-Yield Clinical Pearls for NEET-PG:** 1. **VMAT2 Inhibitors:** Valbenazine and Deutetrabenazine are the current drugs of choice for TD. 2. **Mechanism:** They decrease dopamine levels without blocking the D2 receptor directly, avoiding the worsening of TD. 3. **Historical Context:** Previously, Vitamin E and Benzodiazepines were used, but they lacked robust efficacy. 4. **Pro-tip:** If a patient develops TD, the first step is to taper/stop the offending antipsychotic or switch to **Clozapine** (the antipsychotic with the lowest risk of TD).

Q: An antiepileptic drug can also be used for the treatment of post-herpetic neuralgia and pain due to diabetic neuropathy. Which of the following can be this agent?

Gabapentin. **Explanation:** **Gabapentin** is the correct answer because it is a first-line agent for **neuropathic pain**, including post-herpetic neuralgia (PHN) and painful diabetic neuropathy. 1. **Mechanism of Action:** Despite being a structural analog of GABA, Gabapentin does not act on GABA receptors. Instead, it binds to the **$\alpha_2\delta$ subunit of voltage-gated calcium channels** in the CNS. This binding decreases the entry of calcium into presynaptic terminals, thereby reducing the release of excitatory neurotransmitters like glutamate and substance P, which effectively modulates pain signaling. 2. **Analysis of Incorrect Options:** * **Carbamazepine (A):** While it is an antiepileptic, it is the drug of choice for **Trigeminal Neuralgia**, not typically the first choice for PHN or diabetic neuropathy. * **Lamotrigine (C):** Used primarily for focal seizures, Lennox-Gastaut syndrome, and bipolar disorder. It is not a standard treatment for PHN. * **Primidone (D):** A prodrug converted to phenobarbital; it is used for essential tremors and seizures but has no role in neuropathic pain management. **High-Yield Clinical Pearls for NEET-PG:** * **Pregabalin** shares the same mechanism as Gabapentin but has higher bioavailability and potency. * **Drug of Choice (DOC) Summary:** * Trigeminal Neuralgia: **Carbamazepine** * Post-herpetic Neuralgia: **Gabapentin/Pregabalin** (or TCAs like Amitriptyline) * Diabetic Neuropathy: **Duloxetine** (SNRI), **Gabapentin**, or **Pregabalin**. * **Side Effects:** Gabapentin commonly causes sedation, dizziness, and peripheral edema. It is excreted unchanged by the kidneys, requiring dose adjustment in renal failure.

Q: Phenobarbitone is used in which of the following conditions?

Neonatal jaundice. **Explanation:** **Phenobarbitone** is a barbiturate that acts as a potent **inducer of the hepatic enzyme Glucuronyl transferase**. In the context of neonatal jaundice, it enhances the conjugation of bilirubin and increases its excretion by improving hepatic uptake and bile flow. 1. **Why Neonatal Jaundice is correct:** Phenobarbitone is specifically used in the management of **Crigler-Najjar Syndrome Type II (Arias Syndrome)** and sometimes in prolonged unconjugated hyperbilirubinemia. By inducing glucuronyl transferase, it effectively lowers serum bilirubin levels. However, it is not used for routine physiological jaundice due to its sedative side effects and the time required (3–7 days) to achieve therapeutic efficacy. 2. **Why the other options are incorrect:** * **Organophosphate (OP) and Carbamate poisoning:** These are treated with **Atropine** (muscarinic antagonist) and **Pralidoxime** (PAM - oxime, used only for OP). Phenobarbitone has no role here and may worsen respiratory depression. * **Phenol poisoning:** Management involves immediate decontamination (washing with PEG or water) and supportive care. Phenobarbitone is not an antidote. **High-Yield Clinical Pearls for NEET-PG:** * **Drug of Choice (DOC) for Neonatal Seizures:** Phenobarbitone remains the first-line treatment. * **Crigler-Najjar Differentiation:** A significant drop in bilirubin after Phenobarbitone administration differentiates **Type II** (responsive) from **Type I** (non-responsive). * **Side Effects:** Drowsiness, respiratory depression, and potential long-term effects on cognitive development. * **Enzyme Induction:** It also induces the Cytochrome P450 system, leading to numerous drug interactions.

Q: Nicotine replacement therapy is available in all forms except which of the following?

Tablets. **Explanation:** Nicotine Replacement Therapy (NRT) is designed to deliver nicotine to the systemic circulation to reduce withdrawal symptoms without the harmful toxins found in tobacco smoke. The key pharmacological principle of NRT is **transmucosal or transdermal absorption**, which avoids the **extensive first-pass metabolism** in the liver. **Why "Tablets" is the correct answer:** Nicotine is not administered as an oral tablet (to be swallowed) because it has poor oral bioavailability. When swallowed, nicotine is absorbed into the portal circulation and rapidly metabolized by the liver, making it ineffective. While "sublingual tablets" exist in some global markets (placed under the tongue for mucosal absorption), standard oral tablets are not a recognized form of NRT. **Analysis of Incorrect Options:** * **A. Chewing gum:** One of the most common forms (available in 2mg and 4mg). Nicotine is absorbed through the buccal mucosa. * **B. Lozenges:** These are dissolved slowly in the mouth, allowing for transmucosal absorption. * **C. Patch:** A transdermal delivery system that provides a steady, controlled release of nicotine over 16 or 24 hours, maintaining stable plasma levels. **Clinical Pearls for NEET-PG:** * **Other NRT forms:** Nasal sprays and inhalers (not mentioned in options but clinically used). * **Non-Nicotine Pharmacotherapy:** * **Varenicline:** A partial agonist at the $\alpha4\beta2$ nicotinic acetylcholine receptor (Most effective single agent). * **Bupropion:** An atypical antidepressant (NDRI) that reduces cravings. * **Contraindication:** NRT should be used with caution in patients with recent myocardial infarction (within 2 weeks) or unstable angina.

Q: What is the first active metabolite of chloral hydrate?

Trichloroethanol. **Explanation:** **Chloral hydrate** is a classic sedative-hypnotic prodrug. Its pharmacological activity is almost entirely due to its rapid conversion in the body. **1. Why Trichloroethanol is correct:** Upon ingestion, chloral hydrate is rapidly metabolized by the enzyme **alcohol dehydrogenase** (primarily in the liver and erythrocytes) into **trichloroethanol**. This metabolite is the active moiety responsible for the drug’s sedative and hypnotic effects. It acts similarly to benzodiazepines and barbiturates by enhancing the GABA-A receptor complex. Trichloroethanol is subsequently conjugated with glucuronic acid to form urochloralic acid, which is excreted in the urine. **2. Why the other options are incorrect:** * **Ethanol (A):** While ethanol and chloral hydrate interact (the "Mickey Finn" effect), ethanol is not a metabolite of chloral hydrate. Interestingly, ethanol acts as a cofactor that speeds up the conversion of chloral hydrate to trichloroethanol. * **Dichloroethanol (B) and Monochloroethanol (D):** These are not standard metabolic products of chloral hydrate. The chemical structure of chloral hydrate ($CCl_3CH(OH)_2$) specifically leads to the tri-chlorinated alcohol derivative. **3. High-Yield Clinical Pearls for NEET-PG:** * **The "Mickey Finn":** Combining chloral hydrate with alcohol significantly enhances CNS depression because ethanol increases the NADH/NAD ratio, accelerating the formation of the active trichloroethanol. * **Pear-like Odor:** Chloral hydrate is known for its characteristic pungent, pear-like (or fruity) odor and unpleasant taste. * **Radiology Use:** It was historically used for pediatric sedation during non-invasive procedures (like MRIs), though it has largely been replaced by safer agents due to its narrow therapeutic index and gastric irritation. * **Warfarin Interaction:** It can displace warfarin from plasma albumin, transiently increasing the anticoagulant effect.

Q: Which local anesthetic is known for its differential blockade properties, making it a preferred choice or a differential block option?

Ropivacaine. ### Explanation **Concept of Differential Blockade** Differential blockade refers to the ability of a local anesthetic to selectively block sensory nerve fibers (pain) while sparing motor nerve fibers. This is highly desirable in obstetric analgesia (painless labor) and postoperative pain management, as it allows patients to remain mobile while being pain-free. **Why Ropivacaine is the Correct Answer** Ropivacaine, an amino-amide local anesthetic and the pure S-enantiomer of bupivacaine, is the drug of choice for differential blockade. It is less lipophilic than bupivacaine, which makes it less likely to penetrate the large, myelinated A-alpha motor fibers. Consequently, at lower concentrations (e.g., 0.2%), it provides excellent sensory analgesia with minimal motor impairment. Additionally, it has a higher threshold for cardiotoxicity compared to bupivacaine. **Analysis of Incorrect Options** * **A. Lignocaine:** Known for its rapid onset and intermediate duration. It produces a dense, non-selective block where motor and sensory fibers are affected almost simultaneously. * **C. Bupivacaine:** While it also exhibits some differential block, it is significantly less selective than ropivacaine. It carries a higher risk of cardiotoxicity (due to slow dissociation from sodium channels). * **D. Dibucaine:** An amino-ester anesthetic primarily used for its "Dibucaine Number" to test for atypical pseudocholinesterase deficiency; it is not used for differential blockade in clinical practice. **High-Yield Clinical Pearls for NEET-PG** * **Cardiotoxicity:** Ropivacaine is safer than Bupivacaine because it dissociates faster from cardiac sodium channels. * **Vasoconstriction:** Unlike most local anesthetics (which are vasodilators), Ropivacaine has inherent vasoconstrictive properties. * **S-Enantiomers:** Both Ropivacaine and Levobupivacaine are pure S-enantiomers, designed to reduce the systemic toxicity associated with the racemic mixtures.

Q: Which of the following drugs does not cause sedation?

Buspirone. **Explanation:** The correct answer is **Buspirone**. **1. Why Buspirone is correct:** Buspirone is a non-benzodiazepine anxiolytic that belongs to the **Azapirone** class. Its primary mechanism of action is as a **selective 5-HT1A partial agonist**. Unlike Benzodiazepines (BZDs), it does not interact with the GABA-A receptor complex. Consequently, it lacks the sedative, hypnotic, anticonvulsant, and muscle relaxant properties associated with BZDs. It is specifically used for Generalized Anxiety Disorder (GAD) where daytime alertness is required. **2. Why the other options are incorrect:** * **Nitrazepam & Diazepam:** These are classic **Benzodiazepines** that act as positive allosteric modulators of the GABA-A receptor. They increase the frequency of chloride channel opening, leading to CNS depression, which manifests as significant sedation and hypnosis. * **Zopiclone:** This is a **"Z-drug"** (non-benzodiazepine hypnotic). Although it is chemically different from BZDs, it acts on the same BZ1 (α1 subunit) site of the GABA-A receptor. It is specifically indicated for the short-term treatment of insomnia because of its potent sedative-hypnotic effects. **3. NEET-PG High-Yield Pearls:** * **Buspirone Lag Time:** Unlike BZDs, Buspirone has a slow onset of action (takes 2–4 weeks for full effect); thus, it is not useful for acute anxiety or panic attacks. * **No Abuse Potential:** Buspirone does not cause physical dependence, withdrawal symptoms, or cognitive impairment, making it "driving-friendly." * **Z-drugs (Zolpidem, Zopiclone, Zaleplon):** These are preferred for insomnia as they do not significantly alter the sleep architecture (minimal effect on REM sleep).

Q: Which of the following is true regarding benzodiazepines?

At higher doses, they are less toxic than other sedatives.. ### Explanation **Correct Option: D. At higher doses, they are less toxic than other sedatives.** Benzodiazepines (BZDs) have a high **therapeutic index** compared to older sedatives like barbiturates. This is because BZDs are **GABA-facilitatory**; they increase the *frequency* of chloride channel opening but require the presence of endogenous GABA to function. In contrast, barbiturates are GABA-mimetic (increase *duration* of opening) and can open channels directly at high doses, leading to fatal respiratory depression and coma. Therefore, BZD overdose is rarely fatal unless combined with other CNS depressants [1]. **Why other options are incorrect:** * **A. They alter sleep patterns more than other sedatives:** Incorrect. BZDs actually preserve sleep architecture better than barbiturates. While they do decrease REM sleep and Stage 4 NREM, the effect is less pronounced than with older sedatives. * **B. All benzodiazepines have pharmacologically active metabolites:** Incorrect. Several BZDs bypass phase I oxidative metabolism and are directly conjugated (Phase II) [2]. These are remembered by the mnemonic **LOT**: **L**orazepam, **O**xazepam, and **T**emazepam. They are preferred in elderly patients or those with liver failure [2]. * **C. They induce liver enzymes:** Incorrect. Unlike barbiturates, which are potent inducers of CYP450 enzymes (leading to numerous drug interactions), BZDs do not induce hepatic microsomal enzymes [1]. **High-Yield Clinical Pearls for NEET-PG:** * **Mechanism:** BZDs bind to the BZD-site on the $\text{GABA}_\text{A}$ receptor (between $\alpha$ and $\gamma$ subunits). * **Antidote:** **Flumazenil** is a specific BZD receptor antagonist used for overdose (Note: It can precipitate seizures in dependent patients) [3]. * **Shortest Acting BZD:** Midazolam (used for conscious sedation). * **Longest Acting BZD:** Flurazepam/Diazepam (due to active metabolites) [2].

Question 1

Phenytoin is most widely used for which of the following conditions?

Accepted Answer

All of the above

Answer

Grand mal epilepsy

Answer

Status epilepsy

Answer

Trigeminal neuralgia

Question 2

What is the new drug approved for the treatment of tardive dyskinesia?

Accepted Answer

Valbenazine

Answer

Safinamide

Answer

Tetrabenazine

Answer

Deutetrabenazine

Question 3

Local anesthetics act by:

Accepted Answer

Blocking voltage-gated sodium channels

Answer

Blocking voltage-gated calcium channels

Answer

Blocking voltage-gated potassium channels

Answer

Blocking voltage-gated chloride channels

Question 4

An antiepileptic drug can also be used for the treatment of post-herpetic neuralgia and pain due to diabetic neuropathy. Which of the following can be this agent?

Accepted Answer

Gabapentin

Answer

Carbamazepine

Answer

Lamotrigine

Answer

Primidone

Question 5

Phenobarbitone is used in which of the following conditions?

Accepted Answer

Neonatal jaundice

Answer

Organophosphate poisoning

Answer

Carbamate poisoning

Answer

Phenol poisoning

Question 6

Nicotine replacement therapy is available in all forms except which of the following?

Accepted Answer

Tablets

Answer

Chewing gum

Answer

Lozenges

Answer

Patch

Question 7

What is the first active metabolite of chloral hydrate?

Accepted Answer

Trichloroethanol

Answer

Ethanol

Answer

Dichloroethanol

Answer

Monochloroethanol

Question 8

Which local anesthetic is known for its differential blockade properties, making it a preferred choice or a differential block option?

Accepted Answer

Ropivacaine

Answer

Lignocaine

Answer

Bupivacaine

Answer

Dibucaine

Question 9

Which of the following drugs does not cause sedation?

Accepted Answer

Buspirone

Answer

Nitrazepam

Answer

Zopiclone

Answer

Diazepam

Question 10

Which of the following is true regarding benzodiazepines?

Accepted Answer

At higher doses, they are less toxic than other sedatives.

Answer

They alter sleep patterns more than other sedatives.

Answer

All benzodiazepines have pharmacologically active metabolites.

Answer

They induce liver enzymes.

Central Nervous System Pharmacology — MCQs

Central Nervous System Pharmacology — MCQs

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