Central Nervous System Pharmacology Practice Questions

Q: Which of the following medications is known to cause pancreatitis as a side effect?

Valproate. **Explanation:** **Valproate (Sodium Valproate/Valproic Acid)** is a broad-spectrum antiepileptic and mood stabilizer. It is a well-documented, though rare, cause of **drug-induced acute pancreatitis**. The mechanism is thought to involve the depletion of free radical scavengers or the accumulation of toxic metabolites (like 4-pentenoic acid), leading to direct pancreatic acinar cell injury. This side effect is idiosyncratic, meaning it is not necessarily dose-dependent and can occur at any time during treatment. **Analysis of Incorrect Options:** * **Clonazepam:** A benzodiazepine primarily associated with sedation, ataxia, and cognitive impairment. It does not have a known association with pancreatitis. * **Clozapine:** An atypical antipsychotic known for severe side effects like **agranulocytosis**, seizures, and myocarditis. While it can cause metabolic syndrome and hypertriglyceridemia (which is a risk factor for pancreatitis), it is not the primary drug associated with direct pancreatic toxicity in this list. * **Amisulpride:** An atypical antipsychotic (substituted benzamide) mainly associated with **hyperprolactinemia** and extrapyramidal symptoms. It is not linked to pancreatitis. **High-Yield Clinical Pearls for NEET-PG:** * **Valproate Side Effects (Mnemonic: VALPROATE):** **V**omiting, **A**lopecia, **L**iver toxicity (Hepatotoxicity), **P**ancreatitis/PCOS, **R**etention of weight (Obesity), **O**edema, **A**terixis (due to hyperammonemia), **T**eratogenicity (Neural Tube Defects), **E**nzyme inhibitor. * **Monitoring:** If a patient on Valproate develops acute abdominal pain and vomiting, immediate serum **amylase and lipase** levels must be checked. * **Teratogenicity:** Valproate is the most teratogenic antiepileptic, specifically causing **Spina Bifida**.

Q: Which antidepressant is used in the prophylaxis of migraine?

Amitriptyline. **Explanation:** **Amitriptyline** is a Tricyclic Antidepressant (TCA) and is considered the **first-line antidepressant** for the prophylaxis of migraine. Its efficacy stems from its multi-modal mechanism: it inhibits the reuptake of serotonin and norepinephrine and possesses anticholinergic and antihistaminic properties. In migraine prevention, it is believed to downregulate 5-HT₂ receptors and modulate NMDA receptor-mediated transmission, thereby increasing the threshold for migraine triggers. It is particularly useful in patients who also suffer from tension-type headaches, insomnia, or depression. **Why other options are incorrect:** * **Fluoxetine & Citalopram:** These are Selective Serotonin Reuptake Inhibitors (SSRIs). While they are excellent for depression and anxiety, clinical trials have shown they are generally **ineffective** for migraine prophylaxis compared to TCAs. * **Trazodone:** This is a SARI (Serotonin Antagonist and Reuptake Inhibitor) primarily used for insomnia due to its highly sedative nature. It does not have a proven role in migraine prevention. **High-Yield Clinical Pearls for NEET-PG:** * **DOC for Migraine Prophylaxis:** Propranolol (Beta-blocker) is generally the first choice, but Amitriptyline is the preferred TCA. * **Side Effects of Amitriptyline:** Sedation, weight gain, and anticholinergic effects (dry mouth, blurred vision, urinary retention). It is contraindicated in patients with glaucoma or prostatic hypertrophy. * **Other Prophylactic Agents:** Anticonvulsants (Topiramate, Valproate), Calcium Channel Blockers (Flunarizine), and CGRP antagonists (Erenumab). * **Acute Attack Treatment:** Triptans (5-HT$_{1B/1D}$ agonists) are the drugs of choice for acute migraine relief.

Q: Which of the following antiepileptic drugs is also a free radical scavenger?

Zonisamide. **Explanation:** **Zonisamide** is a broad-spectrum antiepileptic drug with a unique sulfonamide structure. While its primary mechanisms of action include the blockade of **voltage-gated sodium channels** and **T-type calcium channels**, it is distinctively known for its neuroprotective properties. It acts as a **free radical scavenger**, specifically inhibiting lipid peroxidation and scavenging hydroxyl and superoxide radicals. This antioxidant property is a high-yield fact often tested in competitive exams like NEET-PG. **Analysis of Incorrect Options:** * **Levetiracetam (A):** Its primary mechanism is binding to the **SV2A (Synaptic Vesicle Protein 2A)**, which modulates neurotransmitter release. It does not possess significant free radical scavenging activity. * **Topiramate (B):** A multi-mechanistic drug that blocks sodium channels, enhances GABA-A activity, and antagonizes AMPA/Kainate receptors. It is also a weak carbonic anhydrase inhibitor but not a free radical scavenger. * **Gabapentin (D):** It acts by binding to the **α2δ-1 subunit** of voltage-gated calcium channels. It is primarily used for neuropathic pain and focal seizures but lacks antioxidant properties. **Clinical Pearls for NEET-PG:** * **Zonisamide Side Effects:** Notable for causing **weight loss**, nephrolithiasis (kidney stones), and oligohydrosis (decreased sweating), similar to Topiramate. * **Contraindication:** Due to its sulfonamide group, it should be avoided in patients with known **sulfa allergies**. * **Broad Spectrum:** It is effective in focal, generalized tonic-clonic, and even myoclonic seizures.

Q: Varenicline acts by?

Partial nicotine receptor agonist. **Explanation:** **Varenicline** is a high-yield drug in CNS pharmacology, specifically used for **smoking cessation**. Its mechanism of action is centered on its role as a **selective partial agonist** at the **α4β2 nicotinic acetylcholine receptors (nAChR)** located in the brain. 1. **Why Option A is correct:** As a **partial agonist**, varenicline provides a dual benefit. It stimulates the nicotinic receptors enough to maintain a low level of dopamine release, which helps **reduce withdrawal symptoms** and cravings. Simultaneously, because it has a high affinity for the receptor, it blocks nicotine from binding. 2. **Why Option B and C are incorrect:** While varenicline does have "antagonist-like" effects by blocking nicotine, it is pharmacologically classified as a **partial agonist**, not a pure antagonist. Option C is a distractor; although partial agonists exhibit both agonistic and antagonistic properties depending on the presence of a full agonist, the standard pharmacological classification for varenicline is a "Partial Agonist." **High-Yield Clinical Pearls for NEET-PG:** * **Indication:** First-line agent for smoking cessation (more effective than Bupropion). * **Side Effects:** The most common side effect is **nausea**. However, the most serious "red flag" side effects are **neuropsychiatric symptoms**, including suicidal ideation, depression, and vivid dreams/nightmares. * **Comparison:** Unlike **Bupropion** (which inhibits Dopamine and NE reuptake), Varenicline acts directly on the nicotinic receptor. * **Route:** Administered orally.

Q: Which of the following is an ester local anesthetic?

Chlorprocaine. Local anesthetics are clinically classified into two main groups based on their chemical linkage: **Esters** and **Amides**. ### 1. Why Chlorprocaine is Correct **Chlorprocaine** is an ester-linked local anesthetic. The chemical structure of esters contains an ester bond between the aromatic ring and the intermediate chain. A high-yield rule for NEET-PG is the **"i" Rule**: * **Amides** have two "i"s in their name (e.g., Lignocaine, Bupivacaine). * **Esters** have only one "i" in their name (e.g., Procaine, Chlorprocaine, Tetracaine, Cocaine). Chlorprocaine is known for its rapid onset and very short duration of action due to rapid metabolism by plasma pseudocholinesterase. ### 2. Why Other Options are Incorrect * **Bupivacaine (B):** An amide anesthetic. It is highly potent and long-acting but carries a significant risk of cardiotoxicity (S-enantiomer, Levobupivacaine, is less toxic). * **Dibucaine (C):** An amide anesthetic. It is clinically significant for the "Dibucaine Number" test, used to detect atypical pseudocholinesterase deficiency. * **Prilocaine (D):** An amide anesthetic. Its metabolite (o-toluidine) can cause **methemoglobinemia**, which is treated with Methylene Blue. ### 3. High-Yield Clinical Pearls * **Metabolism:** Esters are metabolized by **plasma pseudocholinesterase** (except cocaine, which is partly hepatic). Amides are metabolized by **hepatic microsomal enzymes** (CYP450). * **Allergy:** Allergic reactions are more common with **Esters** due to the metabolite **Para-aminobenzoic acid (PABA)**. * **Cocaine** is the only local anesthetic that is a natural alkaloid and causes vasoconstriction (others are vasodilators).

Q: The topical use of which of the following local anesthetics is not recommended?

Bupivacaine. **Explanation:** The correct answer is **Bupivacaine**. **Why Bupivacaine is not recommended for topical use:** Local anesthetics (LAs) are categorized based on their ability to penetrate mucous membranes and skin. Bupivacaine is a potent, long-acting amide LA with high lipid solubility, but it has **poor mucosal penetration**. More importantly, it carries a significant risk of **cardiotoxicity** (by dissociating slowly from cardiac sodium channels). If used topically on large surfaces or inflamed mucosa, unpredictable systemic absorption could lead to fatal arrhythmias or cardiac arrest before the desired anesthetic effect is achieved. Therefore, it is primarily reserved for infiltration, nerve blocks, and spinal/epidural anesthesia. **Analysis of Incorrect Options:** * **Lidocaine:** The "gold standard" LA. It has excellent mucosal penetration and is widely used topically as a jelly (for catheterization), spray (for intubation), or ointment. * **Cocaine:** A naturally occurring ester and the first LA used clinically. It is a potent topical anesthetic with unique **intrinsic vasoconstrictive** properties, making it useful in ENT surgeries to reduce bleeding. * **Dibucaine:** A quinoline derivative and one of the most potent, long-acting LAs. While too toxic for parenteral use, it is highly effective and commonly used in **topical formulations** (e.g., ointments for hemorrhoids). **High-Yield NEET-PG Pearls:** * **EMLA Cream:** A eutectic mixture of 2.5% Lidocaine and 2.5% Prilocaine used for topical skin anesthesia. * **Cardiotoxicity:** Bupivacaine is the most cardiotoxic LA. Treatment of choice for systemic toxicity (LAST) is **Intralipid (20% Lipid Emulsion)**. * **Benzocaine:** Another LA used *only* topically due to low solubility; however, it can cause **methemoglobinemia**.

Q: Which of the following drugs inhibits the release of calcium from the sarcoplasmic reticulum?

Dantrolene. **Explanation:** **Dantrolene (Correct Answer):** Dantrolene is a peripherally acting muscle relaxant that directly interferes with excitation-contraction coupling in skeletal muscle. It acts by binding to the **Ryanodine Receptor 1 (RyR1)** located on the sarcoplasmic reticulum (SR). This binding inhibits the release of calcium ions from the SR into the cytosol, thereby preventing muscle contraction. This unique mechanism makes it the drug of choice for **Malignant Hyperthermia**, where there is an uncontrolled release of calcium. **Incorrect Options:** * **Caffeine:** Unlike Dantrolene, caffeine actually **stimulates** the Ryanodine receptors, promoting the release of calcium from the SR. In vitro, the "Caffeine-Halothane Contracture Test" is used to diagnose susceptibility to malignant hyperthermia. * **Rocuronium:** This is a **non-depolarizing neuromuscular blocker** that acts at the neuromuscular junction (NMJ) by competitively antagonizing nicotinic acetylcholine receptors ($N_m$). It does not act directly on the SR. * **Succinylcholine:** This is a **depolarizing neuromuscular blocker** that acts as an agonist at $N_m$ receptors, causing persistent depolarization. Notably, it is a known trigger for malignant hyperthermia in susceptible individuals. **NEET-PG High-Yield Pearls:** * **Drug of Choice:** Dantrolene is used for Malignant Hyperthermia, Neuroleptic Malignant Syndrome (NMS), and spasticity associated with upper motor neuron lesions. * **Side Effect:** The most significant chronic side effect of Dantrolene is **hepatotoxicity** (monitor LFTs). * **Malignant Hyperthermia Trigger:** Often triggered by volatile anesthetics (e.g., Halothane) and Succinylcholine due to mutations in the *RYR1* gene.

Question 1

A patient on phenytoin therapy develops depression, for which he was prescribed tricyclic antidepressants. He now complains of lassitude and his Hb reading is 8 gm/dl. What is the next step in the management of this patient?

Accepted Answer

Estimate MCV

Answer

Chest X-ray

Answer

Estimate GGT

Answer

None of the above

Question 2

Which of the following medications is known to cause pancreatitis as a side effect?

Accepted Answer

Valproate

Answer

Clonazepam

Answer

Clozapine

Answer

Amisulpride

Question 3

Which antidepressant is used in the prophylaxis of migraine?

Accepted Answer

Amitriptyline

Answer

Fluoxetine

Answer

Citalopram

Answer

Trazodone

Question 4

Rizatriptan is a drug used for?

Accepted Answer

Acute migraine

Answer

Prophylaxis of migraine

Answer

Cluster headache

Answer

Chronic migraine

Question 5

Which of the following antiepileptic drugs is also a free radical scavenger?

Accepted Answer

Zonisamide

Answer

Levetiracetam

Answer

Topiramate

Answer

Gabapentin

Question 6

Varenicline acts by?

Accepted Answer

Partial nicotine receptor agonist

Answer

Nicotine receptor antagonist

Answer

Both agonist and antagonist at nicotine receptor

Answer

None of the above

Question 7

Which of the following is an ester local anesthetic?

Accepted Answer

Chlorprocaine

Answer

Bupivacaine

Answer

Dibucaine

Answer

Prilocaine

Question 8

The topical use of which of the following local anesthetics is not recommended?

Accepted Answer

Bupivacaine

Answer

Lidocaine

Answer

Cocaine

Answer

Dibucaine

Question 9

Addition of a vasoconstrictor along with local anesthesia causes what?

Accepted Answer

More systemic toxicity

Answer

Fall in blood pressure

Answer

Prolongation of duration of action

Answer

Reduced intensity of block

Question 10

Which of the following drugs inhibits the release of calcium from the sarcoplasmic reticulum?

Accepted Answer

Dantrolene

Answer

Caffeine

Answer

Rocuronium

Answer

Succinylcholine

Central Nervous System Pharmacology — MCQs

Central Nervous System Pharmacology — MCQs

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