Central Nervous System Pharmacology Practice Questions

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.

Q: A patient with ischemic heart disease is diagnosed with migraine. Which drug is indicated in this case?

Butorphanol. **Explanation:** The management of migraine in patients with **Ischemic Heart Disease (IHD)** requires caution because many standard migraine medications cause systemic vasoconstriction, which can exacerbate myocardial ischemia. **Why Butorphanol is correct:** Butorphanol is a mixed opioid agonist-antagonist (κ-agonist and μ-partial agonist/antagonist). Unlike specific anti-migraine drugs, it does not act on serotonin (5-HT) receptors that cause vasoconstriction. It provides potent analgesia for acute migraine attacks without compromising coronary blood flow, making it a safer alternative for patients with cardiovascular contraindications. **Why the other options are incorrect:** * **Triptans (e.g., Sumatriptan):** These are 5-HT$_{1B/1D}$ agonists. While they effectively constrict cranial vessels, they also cause **coronary vasospasm**. They are strictly contraindicated in patients with IHD, Prinzmetal angina, or uncontrolled hypertension. * **Ergotamines:** These act on 5-HT$_{1}$, 5-HT$_{2}$, and α-adrenergic receptors. They are potent, long-acting vasoconstrictors and are contraindicated in IHD and peripheral vascular disease. * **Propranolol:** While used for migraine **prophylaxis**, it is not indicated for the treatment of an acute attack. Furthermore, in certain cardiac conditions (like vasospastic angina), non-selective beta-blockers can worsen coronary vasoconstriction due to unopposed α-activity. **High-Yield Clinical Pearls for NEET-PG:** * **DOC for Acute Migraine:** Triptans (Sumatriptan). * **DOC for Migraine Prophylaxis:** Propranolol (others include Topiramate, Amitriptyline, and Valproate). * **Newer Drugs (Safe in IHD):** **Lasmiditan** (5-HT$_{1F}$ agonist) and **Gepants** (CGRP antagonists like Rimegepant) are preferred modern alternatives for patients with cardiovascular risks as they do not cause vasoconstriction.

Q: Which drug is primarily used for the treatment of absence seizures?

Lamotrigine. **Explanation:** The drug of choice for **Absence Seizures** (Petit Mal) is traditionally **Ethosuximide** (for pure absence) or **Sodium Valproate** (if associated with tonic-clonic seizures). However, among the given options, **Lamotrigine** is the correct answer as it is a broad-spectrum antiepileptic effective against absence seizures. **1. Why Lamotrigine is Correct:** Lamotrigine acts by blocking voltage-gated sodium channels and inhibiting the release of excitatory neurotransmitters (glutamate and aspartate) [1]. It also has some activity against T-type calcium channels, which are central to the pathophysiology of absence seizures. It is considered a first-line alternative, especially in women of childbearing age, due to its better safety profile compared to Valproate. **2. Why Other Options are Incorrect:** * **Carbamazepine & Phenytoin:** These are narrow-spectrum drugs that block sodium channels. They are strictly **contraindicated** in absence seizures as they can paradoxically worsen the condition or precipitate absence status. * **Vigabatrin:** This drug acts by irreversibly inhibiting GABA transaminase. It is primarily used for Infantile Spasms (West Syndrome) and focal seizures [3]. It is not effective for absence seizures. **Clinical Pearls for NEET-PG:** * **Drug of Choice (DOC):** Ethosuximide (Pure Absence); Valproate (Absence + GTCS). * **Mechanism of Ethosuximide:** Inhibition of **T-type Ca²⁺ channels** in thalamic neurons [2]. * **EEG Finding:** Classic **3 Hz spike-and-wave** discharges. * **Avoid in Absence:** Phenytoin, Carbamazepine, Oxcarbazepine, and Tiagabine (they aggravate the seizure) [2]. * **Lamotrigine Side Effect:** Watch for **Stevens-Johnson Syndrome (SJS)**; the dose must be titrated slowly.

Q: Vigabatrin acts by:

GABA transaminase inhibitor. **Explanation:** **Mechanism of Action (The Correct Answer):** Vigabatrin is an antiepileptic drug that acts as an **irreversible inhibitor of GABA transaminase (GABA-T)**. GABA-T is the enzyme responsible for the metabolic degradation of Gamma-Aminobutyric Acid (GABA), the primary inhibitory neurotransmitter in the brain. By inhibiting this enzyme, Vigabatrin significantly increases the concentration of GABA in the synaptic cleft, leading to enhanced inhibitory neurotransmission and suppression of seizure activity. **Analysis of Incorrect Options:** * **Option A (GABA receptor inhibitor):** This would be pro-convulsant (e.g., Bicuculline). Vigabatrin enhances GABAergic tone rather than inhibiting the receptor. * **Option B (Glutamate receptor inhibitor):** While drugs like Perampanel (AMPA antagonist) or Felbamate (NMDA antagonist) work here, Vigabatrin does not affect glutamate receptors directly. * **Option C (GABA transport inhibitor):** This describes the mechanism of **Tiagabine**, which inhibits the GAT-1 transporter to prevent GABA reuptake. **High-Yield Clinical Pearls for NEET-PG:** * **Drug of Choice (DOC):** Vigabatrin is the first-line treatment for **Infantile Spasms (West Syndrome)** associated with **Tuberous Sclerosis**. * **Adverse Effect:** The most characteristic side effect is **permanent bilateral concentric visual field contraction** (visual field defects), necessitating regular perimetry monitoring. * **Mnemonic:** **Vi**gabatrin **G**ABA **T**ransaminase inhibitor (**Vi-GA-T**). * **Excretion:** It is primarily excreted unchanged by the kidneys; dose adjustment is required in renal impairment.

Q: Morphine can be used in all the following conditions except?

Head injury. **Explanation:** **1. Why Head Injury is the Correct Answer (Contraindication):** Morphine is strictly contraindicated in head injuries due to two primary reasons: * **Respiratory Depression & Increased ICP:** Morphine causes respiratory depression, leading to CO₂ retention (hypercapnia). CO₂ is a potent cerebral vasodilator, which increases cerebral blood flow and further elevates **Intracranial Pressure (ICP)**, potentially causing brain herniation. * **Masking of Clinical Signs:** Morphine causes **miosis** (pinpoint pupils) and sedation. This masks critical neurological signs such as pupillary changes and level of consciousness (GCS score), which are essential for monitoring the progression of a head injury. **2. Analysis of Other Options:** * **Asthma:** While Morphine can cause histamine release and worsen bronchospasm, it is a *relative* contraindication compared to the *absolute* danger in head injuries. * **Hypothyroidism:** Patients with myxedema are highly sensitive to the respiratory depressant effects of opioids due to a low metabolic rate, but it is not the primary contraindication in this specific question context. * **Diabetes:** There is no direct contraindication for using Morphine in diabetic patients, although caution is always advised in chronic metabolic conditions. **3. High-Yield Clinical Pearls for NEET-PG:** * **Drug of Choice (DOC):** Morphine is the DOC for pain in **Myocardial Infarction (MI)** and **Acute Left Ventricular Failure (Cardiac Asthma)** because it reduces preload and anxiety. * **Biliary Colic:** Morphine is generally avoided in biliary colic because it causes constriction of the **Sphincter of Oddi** (Pethidine is preferred). * **Triad of Morphine Poisoning:** Coma, Pinpoint pupil, and Depressed respiration. * **Specific Antidote:** **Naloxone** (pure opioid antagonist) is used for acute toxicity.

Q: Which drug is not currently used in the management of Alzheimer's disease?

Tacrine. ### Explanation **1. Why Tacrine is the Correct Answer:** Tacrine was the first centrally acting acetylcholinesterase (AChE) inhibitor approved for Alzheimer’s disease. However, it is **no longer used** in clinical practice due to its significant **hepatotoxicity** (elevation of serum transaminases) and the requirement for frequent dosing (four times daily). Modern clinical guidelines have replaced it with safer, more potent alternatives with better side-effect profiles. **2. Analysis of Incorrect Options:** * **Donepezil (Option C):** A reversible, non-competitive AChE inhibitor. It is the most commonly used drug for Alzheimer’s because of its long half-life (once-daily dosing) and lack of hepatotoxicity. * **Galantamine (Option B):** A competitive AChE inhibitor that also acts as a **nicotinic receptor modulator**, enhancing the action of acetylcholine. It is used for mild-to-moderate Alzheimer's. * **Rivastigmine (Option D):** A "pseudo-irreversible" inhibitor of both AChE and **butyrylcholinesterase**. It is unique because it is available as a **transdermal patch**, which reduces gastrointestinal side effects. **3. High-Yield Clinical Pearls for NEET-PG:** * **Mechanism of Action:** Alzheimer’s is characterized by a cholinergic deficit. These drugs increase acetylcholine levels in the synaptic cleft. * **Memantine:** A NMDA receptor antagonist used for moderate-to-severe Alzheimer’s; it is often combined with Donepezil. * **Side Effects:** Common side effects of AChE inhibitors include "SLUDGE" symptoms (Salivation, Lacrimation, Urination, Diarrhea, GI distress, Emesis) and bradycardia. * **Newer Monoclonal Antibodies:** Keep an eye on **Aducanumab** and **Lecanemab**, which target amyloid-beta plaques.

Question 1

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

Accepted Answer

Bupivacaine

Answer

Lidocaine

Answer

Cocaine

Answer

Dibucaine

Question 2

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 3

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

Accepted Answer

Dantrolene

Answer

Caffeine

Answer

Rocuronium

Answer

Succinylcholine

Question 4

A patient with ischemic heart disease is diagnosed with migraine. Which drug is indicated in this case?

Accepted Answer

Butorphanol

Answer

Propranolol

Answer

Triptans

Answer

Ergotamines

Question 5

Which drug is primarily used for the treatment of absence seizures?

Accepted Answer

Lamotrigine

Answer

Carbamazepine

Answer

Phenytoin

Answer

Vigabatrine

Question 6

What is the primary therapeutic strategy for dopamine deficiency in the substantia nigra in Parkinson's disease?

Accepted Answer

Provision of metabolites in the tyrosine pathway

Answer

Feedback inhibition of dopamine oxidation

Answer

Competitive inhibition of dopamine biosynthesis from histidine

Answer

Stimulation of monoamine oxidase

Question 7

Vigabatrin acts by:

Accepted Answer

GABA transaminase inhibitor

Answer

GABA receptor inhibitor

Answer

Glutamate receptor inhibitor

Answer

GABA transport inhibitor

Question 8

Which of the following statements regarding the action of local anesthetics is true?

Accepted Answer

In areas with lower pH, the effectiveness of anesthetic agents is reduced.

Answer

There is little relation between H ion concentration and anesthetic activity.

Answer

There is no correlation between H ion concentration and anesthetic activity.

Question 9

Morphine can be used in all the following conditions except?

Accepted Answer

Head injury

Answer

Asthma

Answer

Hypothyroidism

Answer

Diabetes

Question 10

Which drug is not currently used in the management of Alzheimer's disease?

Accepted Answer

Tacrine

Answer

Galantamine

Answer

Donepezil

Answer

Rivastigmine

Central Nervous System Pharmacology — MCQs

Central Nervous System Pharmacology — MCQs

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