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 of the following is an ester-linked local anesthetic?

Cocaine. **Explanation:** Local anesthetics (LAs) are chemically classified into two categories based on the linkage between their aromatic and amine groups: **Esters** and **Amides**. **1. Why Cocaine is Correct:** Cocaine is a naturally occurring **ester-linked** local anesthetic. Esters are metabolized by plasma pseudocholinesterase and generally have a shorter duration of action (except for tetracaine). Cocaine is unique among LAs because it is the only one that possesses intrinsic vasoconstrictive properties by inhibiting the reuptake of norepinephrine. **2. Why the Other Options are Incorrect:** * **Lidocaine, Bupivacaine, and Dibucaine** are all **amide-linked** local anesthetics. Amides are metabolized primarily in the liver by cytochrome P450 enzymes and are generally more stable with a longer half-life than esters. **3. High-Yield NEET-PG Clinical Pearls:** * **The "i" Rule:** A simple mnemonic to differentiate the two is that all **Amides** have two "i"s in their name (L**i**doca**i**ne, Bup**i**vaca**i**ne, D**i**buca**i**ne, Pr**i**loca**i**ne, Rop**i**vaca**i**ne), whereas **Esters** have only one "i" (Cocaine, Procaine, Benzocaine, Tetracaine). * **Allergy:** Hypersensitivity reactions are more common with esters due to the production of **Para-aminobenzoic acid (PABA)** during metabolism. True allergy to amides is extremely rare. * **Dibucaine:** It is the most potent and toxic long-acting amide. The "Dibucaine number" is clinically used to detect atypical pseudocholinesterase deficiency. * **Bupivacaine:** Notable for its significant cardiotoxicity (S-enantiomer, Levobupivacaine, is less toxic).

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: Which of the following statements about dezocine is true?

Dezocine does not increase histamine release.. **Explanation:** Dezocine is a synthetic opioid analgesic with a unique pharmacological profile, classified as an **opioid agonist-antagonist**. It acts primarily as a partial agonist at **$\mu$ (mu)** receptors and an antagonist at **$\kappa$ (kappa)** receptors. **1. Why Option D is Correct:** Unlike traditional opioids like morphine or codeine, dezocine **does not cause significant histamine release**. This makes it clinically advantageous in patients with reactive airway diseases (like asthma) or those prone to hemodynamic instability, as it lacks the histamine-mediated side effects of itching, flushing, and hypotension. **2. Analysis of Incorrect Options:** * **Option A:** Dezocine has a **rapid onset of action**, typically within 15–30 minutes after intramuscular administration, which is comparable to or slightly faster than morphine. * **Option B:** Dezocine is **equipotent to morphine** (10 mg of dezocine $\approx$ 10 mg of morphine) in terms of analgesic efficacy for postoperative pain. * **Option C:** Dezocine acts on **opioid receptors** ($\mu$ and $\kappa$), not GABA receptors. GABA receptors are the primary targets for benzodiazepines and barbiturates. **High-Yield Clinical Pearls for NEET-PG:** * **Ceiling Effect:** Like other mixed agonist-antagonists, dezocine exhibits a "ceiling effect" on respiratory depression, making it safer than pure $\mu$-agonists in overdose. * **Mechanism:** It also inhibits the reuptake of norepinephrine and serotonin, contributing to its analgesic profile. * **Clinical Use:** Primarily used for postoperative pain and balanced anesthesia. It is less likely to cause physical dependence compared to morphine.

Q: How do local anesthetics work?

Block the influx of sodium into the cell. ### Explanation **Mechanism of Action:** Local anesthetics (LAs) work by reversibly binding to the **intracellular** portion of **voltage-gated sodium channels**. When an LA molecule enters the nerve fiber and binds to these channels, it stabilizes them in an inactivated state. This prevents the **influx of sodium ions** into the cell, which is essential for depolarization. Without depolarization, the action potential cannot be generated or conducted along the nerve membrane, resulting in a functional "block." **Analysis of Options:** * **Option A & C:** These describe the mechanisms of general anesthetics or CNS-acting drugs (like GABA agonists). LAs act primarily on the peripheral nerve conduction pathway, not by modulating neurotransmitter release at the synapse. * **Option D:** Inhibition of sodium *efflux* (via the Na+/K+ ATPase pump) would actually lead to intracellular sodium accumulation and would not prevent the rapid depolarization required for an action potential. **High-Yield Clinical Pearls for NEET-PG:** * **State-Dependent Block:** LAs have a higher affinity for sodium channels that are in the **open or inactivated states** (active firing) rather than the resting state. * **Differential Block:** Small, myelinated fibers (A-delta) and unmyelinated fibers (C-fibers) are blocked before large, myelinated motor fibers. The sequence of blockade is typically: **Pain > Temperature > Touch > Pressure > Motor.** * **Chemistry:** LAs are weak bases. In acidic environments (e.g., infected tissue), they become ionized and cannot cross the lipid membrane, leading to reduced efficacy. * **Bupivacaine:** Notable for being the most cardiotoxic LA; Intralipid (20% lipid emulsion) is the antidote for Local Anesthetic Systemic Toxicity (LAST).

Question 1

Alpha adrenergic agonists are used in combination with local anesthetics to:

Accepted Answer

Increase the concentration of local anesthetic at the receptor site.

Answer

Increase the rate of liver metabolism of local anesthetic.

Answer

Stimulate myocardial contraction.

Answer

Increase vascular absorption of local anesthetic.

Question 2

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 3

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

Accepted Answer

Valproate

Answer

Clonazepam

Answer

Clozapine

Answer

Amisulpride

Question 4

Which of the following is an ester-linked local anesthetic?

Accepted Answer

Cocaine

Answer

Lidocaine

Answer

Bupivacaine

Answer

Dubicaine

Question 5

Which antidepressant is used in the prophylaxis of migraine?

Accepted Answer

Amitriptyline

Answer

Fluoxetine

Answer

Citalopram

Answer

Trazodone

Question 6

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

Accepted Answer

Bupivacaine

Answer

Lidocaine

Answer

Cocaine

Answer

Dibucaine

Question 7

Rizatriptan is a drug used for?

Accepted Answer

Acute migraine

Answer

Prophylaxis of migraine

Answer

Cluster headache

Answer

Chronic migraine

Question 8

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

Accepted Answer

Zonisamide

Answer

Levetiracetam

Answer

Topiramate

Answer

Gabapentin

Question 9

Which of the following statements about dezocine is true?

Accepted Answer

Dezocine does not increase histamine release.

Answer

Dezocine acts slower than morphine.

Answer

Dezocine is less potent than morphine.

Answer

Dezocine acts on GABA receptors.

Question 10

How do local anesthetics work?

Accepted Answer

Block the influx of sodium into the cell

Answer

Block the release of neurotransmitters

Answer

Increase the release of inhibitory neurotransmitters

Answer

Inhibit the efflux of sodium from neurons

Central Nervous System Pharmacology — MCQs

Central Nervous System Pharmacology — MCQs

On this page

Practice by Chapter

Want unlimited practice?