Central Nervous System Pharmacology Practice Questions

Q: Which of the following statements regarding cocaine is true, except?

Has a half-life of 3 hours. **Explanation:** Cocaine is a potent sympathomimetic alkaloid derived from *Erythroxylum coca*. Understanding its pharmacokinetics and clinical profile is high-yield for NEET-PG. **1. Why Option B is the correct answer (The Exception):** The statement that cocaine has a half-life of 3 hours is **incorrect**. Cocaine has a very short half-life, typically ranging from **30 to 90 minutes**. It is rapidly metabolized by plasma and liver esterases (pseudocholinesterase) into metabolites like benzoylecgonine, which can be detected in urine for several days. **2. Analysis of other options:** * **Option A (Tachycardia and Hypertension):** This is **true**. Cocaine blocks the reuptake of norepinephrine, dopamine, and serotonin at nerve terminals. The resulting excess of norepinephrine causes potent stimulation of alpha and beta-adrenergic receptors, leading to vasoconstriction, hypertension, and tachycardia. * **Option C (No Antidote):** This is **true**. There is no specific pharmacological antagonist (antidote) for cocaine. Management is primarily supportive, focusing on benzodiazepines (to control seizures and agitation) and cooling measures. * **Option D (Snorting):** This is **true**. Cocaine is commonly administered via "snorting" (intranasal insufflation), though it can also be taken intravenously or smoked (as "crack" cocaine). **Clinical Pearls for NEET-PG:** * **Mechanism:** Indirect sympathomimetic (reuptake inhibitor). * **Local Anesthetic:** It is the only local anesthetic with **intrinsic vasoconstrictive** properties (due to NET inhibition). * **Contraindication:** Never use **pure Beta-blockers** (e.g., Propranolol) in cocaine toxicity; it leads to "unopposed alpha-stimulation," causing a hypertensive crisis. * **Cardiovascular Risk:** Cocaine-induced coronary vasospasm can lead to Myocardial Infarction (MI) even in young patients.

Q: Which local anesthetic raises blood pressure instead of tending to cause a fall?

Cocaine. **Explanation:** The correct answer is **Cocaine**. **1. Why Cocaine is correct:** Most local anesthetics (LAs) are vasodilators and can cause hypotension by relaxing vascular smooth muscle and depressing myocardial contractility. Cocaine is the unique exception. It acts as a **sympathomimetic** by blocking the reuptake of norepinephrine (NE) at sympathetic nerve endings (NET inhibition). This leads to an accumulation of NE in the synaptic cleft, causing potent vasoconstriction, tachycardia, and a significant **increase in blood pressure**. **2. Why the other options are incorrect:** * **Lignocaine (Lidocaine):** The most widely used LA; it causes vasodilation and can lead to hypotension if absorbed systemically in large doses. * **Procaine:** An ester-linked LA with significant vasodilatory properties and a short duration of action. * **Dibucaine:** A potent, long-acting amide LA (often used in spinal anesthesia) that, like others, typically causes a fall in BP due to sympathetic blockade. **3. NEET-PG High-Yield Pearls:** * **Vasoconstriction:** Cocaine is the only naturally occurring local anesthetic and the only one that causes vasoconstriction. * **Clinical Use:** Due to its vasoconstrictive property, it is used topically in ENT surgeries to reduce bleeding (e.g., nasal packing). * **Cardiotoxicity:** While most LAs cause bradycardia, cocaine causes tachycardia and arrhythmias. * **Adrenaline Interaction:** Never co-administer adrenaline with cocaine, as it can lead to a hypertensive crisis or fatal arrhythmias. * **Metabolism:** Unlike other esters (metabolized by plasma pseudocholinesterase), cocaine is primarily metabolized in the liver.

Q: Which of the following is the most efficacious triptan for rapid relief of acute migraine attack?

Rizatriptan. **Explanation:** **Rizatriptan** is considered the most efficacious oral triptan for the rapid relief of acute migraine. The clinical superiority of Rizatriptan (10 mg) lies in its **pharmacokinetic profile**: it has a faster onset of action (Tmax of ~1 hour) and higher oral bioavailability compared to the prototype drug, Sumatriptan. Clinical trials consistently show that Rizatriptan achieves higher rates of "pain-free status" at 2 hours than most other oral triptans. **Analysis of Options:** * **Sumatriptan (Option A):** The first-generation triptan. While the subcutaneous route is the fastest overall, its **oral** form has low bioavailability (~15%) and a slower onset than Rizatriptan. * **Almotriptan (Option B):** It has better bioavailability than Sumatriptan and a better side-effect profile, but it does not surpass Rizatriptan in terms of speed or peak efficacy. * **Naratriptan (Option D):** Known for having a longer half-life and fewer side effects, but it has a **slow onset of action** and lower potency. It is typically used for migraines with a longer duration or to prevent recurrence, rather than rapid relief. **High-Yield NEET-PG Pearls:** * **Mechanism of Action:** Triptans are **5-HT$_{1B/1D}$ agonists**. They cause cranial vasoconstriction (1B) and inhibit the release of pro-inflammatory neuropeptides (CGRP, Substance P) from trigeminal nerve endings (1D). * **Fastest Route:** Subcutaneous Sumatriptan is the fastest overall delivery method. * **Longest Acting:** **Frovatriptan** has the longest half-life (~26 hours), followed by Naratriptan. * **Contraindications:** Due to vasoconstrictive effects, triptans are contraindicated in patients with Ischemic Heart Disease (IHD), Prinzmetal angina, and uncontrolled hypertension.

Q: Which of the following statements is FALSE about the drug treatment with Memantine?

It is an NMDA receptor agonist. **Explanation:** The correct answer is **D** because Memantine is an **NMDA receptor antagonist**, not an agonist [1], [2]. **1. Why Option D is False (The Mechanism):** Memantine is a low-to-moderate affinity, non-competitive **NMDA (N-methyl-D-aspartate) receptor antagonist** [1]. In Alzheimer’s disease, overstimulation of NMDA receptors by glutamate leads to excessive calcium influx, causing "excitotoxicity" and neuronal death. Memantine binds to these receptors to block this pathological activation, thereby preserving neuronal function [3]. **2. Analysis of Other Options:** * **Option A (Neuroprotective):** By preventing glutamate-induced excitotoxicity and reducing calcium-mediated cell death, Memantine exerts a neuroprotective effect on surviving neurons [3]. * **Option B (Long Half-life):** Memantine has a clinically significant long terminal half-life of approximately **60 to 80 hours**, allowing for once-daily dosing. * **Option C (Moderate Dementia):** Memantine is specifically FDA-approved for the treatment of **moderate-to-severe** Alzheimer’s disease [3]. It is often used as monotherapy or in combination with Donepezil (an acetylcholinesterase inhibitor) [1]. **High-Yield Clinical Pearls for NEET-PG:** * **Indication:** Unlike Donepezil (used for mild-to-severe), Memantine is typically reserved for **moderate-to-severe** cases [3]. * **Side Effects:** Generally well-tolerated; the most common side effects are dizziness, headache, and confusion [3]. * **Combination Therapy:** The combination of Memantine + Donepezil (Namzaric) shows synergistic benefits in advanced dementia [1]. * **Excretion:** It is primarily excreted unchanged by the kidneys; dose adjustment is required in severe renal impairment.

Q: Levosulpiride acts as an antagonist of which central dopamine receptor?

D2. **Explanation:** **Levosulpiride** is the levo-enantiomer of sulpiride, belonging to the **substituted benzamide** class of drugs. Its primary mechanism of action is the selective and potent **antagonism of central and peripheral Dopamine D2 receptors.** 1. **Why D2 is correct:** At low doses, levosulpiride acts as an antagonist at presynaptic D2 receptors (increasing dopamine release), while at higher doses, it blocks postsynaptic D2 receptors. In the CNS, this blockade provides antipsychotic and antidepressant effects. Peripherally, its D2 antagonism in the gastrointestinal tract makes it a potent **prokinetic agent**, used for dyspepsia and GERD. 2. **Why other options are incorrect:** * **D1:** Levosulpiride has negligible affinity for D1 receptors. D1 receptors are primarily involved in the direct pathway of the basal ganglia. * **D3 and D4:** While some atypical antipsychotics (like Clozapine) have high affinity for D4, and others (like Amisulpride) affect D3, Levosulpiride is highly selective for the **D2** subtype. **High-Yield Clinical Pearls for NEET-PG:** * **Dual Action:** It is used both as an **atypical antipsychotic** and a **prokinetic**. * **Adverse Effects:** Due to D2 blockade in the tuberoinfundibular pathway, it can cause **hyperprolactinemia**, leading to galactorrhea, amenorrhea, and gynecomastia. * **Extrapyramidal Symptoms (EPS):** Although it is an "atypical" agent with lower risk, it can still cause Parkinsonian symptoms or tardive dyskinesia at high doses. * **Comparison:** Unlike Metoclopramide, Levosulpiride is more selective and has a better safety profile regarding CNS side effects at prokinetic doses.

Q: Tolerance develops to all of the following actions of opioids except:

Miosis. **Explanation:** Tolerance is a pharmacological phenomenon where a subject’s reaction to a specific drug concentration is progressively reduced, requiring an increase in dosage to achieve the same effect. In the case of opioids, tolerance develops at different rates for different physiological effects. **Why Miosis is the Correct Answer:** Tolerance develops to almost all pharmacological actions of opioids **EXCEPT** for two specific effects: **Miosis** (pinpoint pupils) and **Constipation**. * **Mechanism:** Miosis occurs due to the stimulation of the Edinger-Westphal nucleus of the IIIrd cranial nerve. The lack of tolerance to miosis is clinically significant because it serves as a reliable diagnostic marker for opioid overdose, even in chronic addicts. **Analysis of Incorrect Options:** * **Analgesia (B):** Tolerance develops rapidly to the pain-relieving effects of opioids. This often necessitates dose escalation in chronic pain management or palliative care. * **Euphoria (C):** Tolerance to the "high" or euphoric effect develops very quickly, which is a primary driver for dose escalation in opioid use disorder. * **Nausea and Vomiting (D):** These effects are mediated by the stimulation of the Chemoreceptor Trigger Zone (CTZ). With repeated administration, most patients develop tolerance to these emetic effects. **High-Yield Clinical Pearls for NEET-PG:** * **Mnemonic for No Tolerance:** Remember **"M.C."** (like a Master of Ceremonies) — **M**iosis and **C**onstipation. * **Rate of Tolerance:** High tolerance develops to Analgesia, Euphoria, Respiratory depression, and Sedation. Moderate tolerance develops to Bradycardia. * **Lethality:** Because tolerance to respiratory depression is high but not absolute, an addict who relapses and takes their previous high dose is at extreme risk of fatal respiratory failure. * **Triad of Opioid Poisoning:** Coma, Pinpoint pupil, and Respiratory depression.

Q: What is the maximum safe dose of lignocaine with adrenaline for local blocks in ophthalmic surgeries?

7 mg/kg. **Explanation:** The maximum safe dose of local anesthetics is a high-yield topic in both Ophthalmology and Anesthesia. The dosage depends primarily on whether a vasoconstrictor (like adrenaline) is added to the solution. **1. Why 7 mg/kg is correct:** Lignocaine (Lidocaine) is an amide-type local anesthetic. When used **with adrenaline** (typically 1:100,000 or 1:200,000 concentration), the adrenaline causes local vasoconstriction. This slows down the systemic absorption of the drug, reduces peak plasma levels, and prolongs the duration of the block. This decreased rate of absorption allows for a higher safe threshold, which is **7 mg/kg**. **2. Analysis of Incorrect Options:** * **3 mg/kg (Option A):** This is significantly below the safe threshold for lignocaine and is not a standard limit for this drug. * **5 mg/kg (Option B):** This is the maximum safe dose for **plain lignocaine** (without adrenaline). Without a vasoconstrictor, the drug is absorbed more rapidly into the systemic circulation, increasing the risk of systemic toxicity (LAST). * **10 mg/kg (Option D):** This dose exceeds the safety limit for lignocaine and carries a high risk of Central Nervous System (CNS) and cardiovascular toxicity. **3. Clinical Pearls for NEET-PG:** * **Maximum Absolute Dose:** Regardless of weight, the total dose of lignocaine with adrenaline should generally not exceed **500 mg** in an adult. * **Ophthalmic Context:** In ophthalmic blocks (Peribulbar/Retrobulbar), a mixture of Lignocaine (2%) and Bupivacaine (0.5%) is often used. Bupivacaine provides a longer duration of action but has a lower safety margin (**2 mg/kg**). * **Hyaluronidase:** Often added to ophthalmic blocks to increase tissue permeability and speed up the onset of the block, though it does not affect the maximum safe dose of the anesthetic itself. * **Early signs of toxicity:** Perioral numbness, metallic taste, and tremors.

Q: What is the antiepileptic of choice in post-diabetic peripheral neuropathy?

Pregabalin. **Explanation:** The management of **Painful Diabetic Peripheral Neuropathy (DPN)** involves several classes of drugs, but **Pregabalin** is currently considered the first-line antiepileptic of choice. **Why Pregabalin is Correct:** Pregabalin is a calcium channel modulator that binds to the **̡2-̈́ subunit of voltage-gated calcium channels** in the CNS. This reduces the release of excitatory neurotransmitters (like glutamate and substance P), thereby inhibiting pain signaling [1]. It is FDA-approved for DPN and is preferred due to its superior safety profile, predictable pharmacokinetics, and faster onset of action compared to other agents. **Analysis of Incorrect Options:** * **Amitriptyline (Option B):** While highly effective and often used as a first-line agent (especially in resource-limited settings), it is a **Tricyclic Antidepressant (TCA)**, not an antiepileptic. It is also limited by anticholinergic side effects (dry mouth, urinary retention) and cardiac risks. * **Carbamazepine (Option C):** This is the drug of choice for **Trigeminal Neuralgia**. It is generally not preferred for DPN due to its side effect profile and drug-drug interactions. * **Duloxetine (Option D):** This is an **SNRI** (Serotonin-Norepinephrine Reuptake Inhibitor). Like Amitriptyline, it is a first-line treatment for DPN but does not belong to the antiepileptic class. **High-Yield Clinical Pearls for NEET-PG:** * **First-line classes for DPN:** Gabapentinoids (Pregabalin/Gabapentin), SNRIs (Duloxetine), and TCAs (Amitriptyline). * **Gabapentin vs. Pregabalin:** Pregabalin has better bioavailability and a more linear dose-response curve than Gabapentin [1]. * **Side Effects:** Dizziness and somnolence are the most common side effects of Pregabalin. * **DOC for Trigeminal Neuralgia:** Carbamazepine. * **DOC for Post-herpetic Neuralgia:** Gabapentin/Pregabalin or Topical Lidocaine.

Q: Beta-carboline at benzodiazepine receptors acts as?

Inverse agonist. **Explanation:** The Benzodiazepine (BZD) receptor is a modulatory site on the **GABA-A receptor-chloride channel complex**. Drugs acting at this site are classified based on their intrinsic activity: 1. **Inverse Agonists (Beta-carbolines):** These bind to the BZD receptor but produce effects **opposite** to those of benzodiazepines. While BZDs increase chloride channel opening frequency (facilitating GABA), beta-carbolines decrease it. This results in **anxiogenic** (anxiety-inducing) and **pro-convulsant** effects. 2. **Agonists (Benzodiazepines like Diazepam):** These facilitate GABA action, leading to sedation, anxiolysis, and anticonvulsant effects. 3. **Antagonists (Flumazenil):** These have no intrinsic activity but competitively block both agonists and inverse agonists. Flumazenil is used clinically to reverse BZD overdose. 4. **Physiological Antagonists:** This term refers to two drugs acting on different receptors to produce opposite physiological effects (e.g., Histamine and Adrenaline on bronchial smooth muscle). Beta-carbolines act on the *same* receptor as BZDs, making this option incorrect. **High-Yield Clinical Pearls for NEET-PG:** * **Flumazenil** is the specific antidote for BZD poisoning but can precipitate seizures in chronic BZD users or TCA overdose. * **GABA-A** is an ionotropic receptor (chloride channel), while **GABA-B** is a metabotropic G-protein coupled receptor (baclofen acts here). * **Z-drugs** (Zolpidem, Zopiclone) are selective agonists at the **alpha-1 subunit** of the GABA-A receptor, primarily used for hypnosis without significant anxiolysis.

Question 1

Which of the following statements regarding cocaine is true, except?

Accepted Answer

Has a half-life of 3 hours

Answer

Causes tachycardia and hypertension

Answer

Has no antidote

Answer

Can be taken by snorting

Question 2

Which local anesthetic raises blood pressure instead of tending to cause a fall?

Accepted Answer

Cocaine

Answer

Dibucaine

Answer

Lignocaine

Answer

Procaine

Question 3

Which of the following is the most efficacious triptan for rapid relief of acute migraine attack?

Accepted Answer

Rizatriptan

Answer

Sumatriptan

Answer

Almotriptan

Answer

Naratriptan

Question 4

Which of the following statements is FALSE about the drug treatment with Memantine?

Accepted Answer

It is an NMDA receptor agonist

Answer

It is neuroprotective

Answer

It has a long half-life

Answer

It is used in the treatment of moderate dementia

Question 5

Levosulpiride acts as an antagonist of which central dopamine receptor?

Accepted Answer

D2

Answer

D1

Answer

D3

Answer

D4

Question 6

Tolerance develops to all of the following actions of opioids except:

Accepted Answer

Miosis

Answer

Analgesia

Answer

Euphoria

Answer

Nausea and vomiting

Question 7

What is the maximum safe dose of lignocaine with adrenaline for local blocks in ophthalmic surgeries?

Accepted Answer

7 mg/kg

Answer

3 mg/kg

Answer

5 mg/kg

Answer

10 mg/kg

Question 8

What is the antiepileptic of choice in post-diabetic peripheral neuropathy?

Accepted Answer

Pregabalin

Answer

Amitriptyline

Answer

Carbamazepine

Answer

Duloxetine

Question 9

An antiepileptic drug was found successful for treatment of tonic hind limb extension (THLE). In which type of seizure can this drug be used?

Accepted Answer

General tonic clonic seizures

Answer

Absent seizures

Answer

Myoclonic seizures

Answer

Status epilepticus

Question 10

Beta-carboline at benzodiazepine receptors acts as?

Accepted Answer

Inverse agonist

Answer

Agonist

Answer

Antagonist

Answer

Physiological antagonist

Central Nervous System Pharmacology — MCQs

Central Nervous System Pharmacology — MCQs

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