Central Nervous System Pharmacology Practice Questions

Q: Which local anesthetic agent causes cutaneous vasoconstriction?

Ropivacaine. **Explanation:** The primary mechanism of most local anesthetics (LAs) involves the blockade of sodium channels, which typically results in **vasodilation** at clinical concentrations. This occurs due to the relaxation of vascular smooth muscle. However, **Ropivacaine** is a unique long-acting amide local anesthetic that possesses intrinsic **cutaneous vasoconstrictive** properties. **Why Ropivacaine is Correct:** Ropivacaine causes vasoconstriction at concentrations commonly used for clinical anesthesia (up to 1%). This intrinsic property reduces its own systemic absorption, prolongs the duration of action, and decreases the risk of systemic toxicity. It is chemically an S-enantiomer, which contributes to its lower cardiotoxicity compared to Bupivacaine. **Why the Other Options are Incorrect:** * **Lidocaine (Option A):** A prototype amide LA that causes significant vasodilation. It is often formulated with epinephrine to counteract this effect. * **Mepivacaine (Option C):** While it has less vasodilatory effect than lidocaine, it does not produce significant vasoconstriction like Ropivacaine. * **Procaine (Option D):** An ester-type LA known for being a potent vasodilator; it has a very short duration of action because it is rapidly cleared from the site of injection. **High-Yield Clinical Pearls for NEET-PG:** * **Exceptions to Vasodilation:** Only three local anesthetics cause significant vasoconstriction: **Cocaine** (most potent), **Ropivacaine**, and **Levobupivacaine**. * **Cocaine’s Mechanism:** Unlike Ropivacaine, Cocaine causes vasoconstriction by inhibiting the reuptake of norepinephrine at sympathetic nerve endings. * **Safety Profile:** Ropivacaine is preferred over Bupivacaine for epidural labor analgesia because it produces a "differential block" (greater sensory block with minimal motor block) and has a higher threshold for CNS and cardiac toxicity.

Q: A very potent and short-acting benzodiazepine was given to a patient for the purpose of causing hypnosis, but the drug caused psychiatric disturbances. Which of the following could be the hypnotic used?

Triazolam. **Explanation:** The correct answer is **Triazolam**. **1. Why Triazolam is correct:** Triazolam is an ultra-short-acting benzodiazepine (half-life: 2–3 hours) used primarily for the induction of sleep. Because of its high potency and rapid elimination, it is uniquely associated with a high incidence of **psychiatric disturbances**, including daytime anxiety, amnesia, confusion, and "rebound insomnia." More importantly, it can cause severe behavioral side effects such as agitation, hallucinations, and even paranoia (often referred to as the "Triazolam syndrome"). Due to these adverse psychiatric effects, its use has been restricted or banned in several countries. **2. Why other options are incorrect:** * **Flurazepam:** This is a long-acting benzodiazepine (half-life >50 hours due to active metabolites). Its primary side effect is "hangover" or excessive daytime sedation, rather than acute psychiatric disturbances. * **Nitrazepam:** An intermediate-acting benzodiazepine. While it can cause morning grogginess, it does not share the specific high-potency, short-acting profile linked to the psychiatric agitation seen with Triazolam. * **Temazepam:** An intermediate-acting drug (half-life 8–12 hours). It is metabolized by conjugation and is generally better tolerated in terms of behavioral side effects compared to Triazolam. **High-Yield Clinical Pearls for NEET-PG:** * **Shortest Acting BZD:** Midazolam (used for anesthesia) and Triazolam (used for hypnosis). * **Longest Acting BZD:** Flurazepam and Quazepam. * **BZDs safe in Liver Failure:** Remember the mnemonic **LOT** (Lorazepam, Oxazepam, Temazepam) as they undergo direct glucuronidation and have no active metabolites. * **Triazolam specific side effect:** Anterograde amnesia is more common with Triazolam than with most other oral BZDs.

Q: The antiepileptic drug lacosamide acts by:

Inhibiting CRMP protein. **Explanation:** **Lacosamide** is a third-generation antiepileptic drug with a unique dual mechanism of action. Its primary mechanism is the **selective enhancement of slow inactivation of voltage-gated sodium channels**, which stabilizes hyperexcitable neuronal membranes. However, it also binds to **Collapsin Response Mediator Protein-2 (CRMP-2)**. CRMP-2 is a phosphoprotein involved in neuronal differentiation and axonal outgrowth; by modulating this protein, lacosamide is thought to exert neuroprotective effects and interfere with the process of epileptogenesis. **Analysis of Options:** * **Option A (Inhibiting synaptic vesicular protein):** This describes the mechanism of **Levetiracetam** and **Brivaracetam**, which bind to the **SV2A** protein to modulate neurotransmitter release. * **Option C (Inhibiting GABA metabolism):** This refers to drugs like **Vigabatrin** (inhibits GABA-transaminase) or **Tiagabine** (inhibits GABA reuptake via GAT-1). * **Option D (Inhibiting glutamate release):** While many drugs indirectly reduce glutamate (like Lamotrigine via sodium channel blockade), this is not the specific defining mechanism associated with Lacosamide’s interaction with CRMP-2. **High-Yield Clinical Pearls for NEET-PG:** * **Indications:** Approved for focal-onset (partial) seizures in patients aged 1 month and older. * **Pharmacokinetics:** It has excellent bioavailability (100%) and minimal drug-drug interactions, as it does not significantly induce or inhibit Cytochrome P450 enzymes. * **Adverse Effects:** A characteristic side effect is **PR interval prolongation** on ECG; therefore, it should be used with caution in patients with known conduction problems. * **Schedule:** It is a Schedule V controlled substance due to a low potential for abuse (euphoria).

Q: Which drug has inverse agonist activity at benzodiazepine receptors?

Beta carboline. **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. **Agonists (e.g., Diazepam):** Increase the frequency of chloride channel opening, leading to CNS depression (anxiolysis, sedation). 2. **Antagonists (e.g., Flumazenil):** Occupy the receptor with zero intrinsic activity, blocking the effects of both agonists and inverse agonists. 3. **Inverse Agonists (e.g., Beta-carbolines):** These produce effects **opposite** to those of BZD agonists. By reducing the frequency of chloride channel opening, they cause CNS stimulation, manifesting as intense anxiety, restlessness, and convulsions (pro-convulsant). **Analysis of Options:** * **B. Beta-carboline (Correct):** It is the classic example of a BZD inverse agonist. It decreases GABA-mediated chloride conductance. * **A. Flumazenil:** It is a **competitive antagonist** at BZD receptors. It is used to reverse BZD overdose but does not possess inverse agonist activity. * **C. Naltrexone:** It is an **opioid receptor antagonist** used in the management of opioid addiction and alcohol dependence; it has no action at BZD receptors. * **D. Zopiclone:** It is a **non-benzodiazepine hypnotic** ("Z-drug"). Despite a different chemical structure, it acts as a full **agonist** at the BZD-1 (alpha-1 subunit) receptor. **High-Yield Pearls for NEET-PG:** * **Flumazenil** has a shorter half-life than most BZDs; watch for "re-sedation" in clinical scenarios. * **Z-drugs** (Zolpidem, Zopiclone, Zaleplon) are preferred for insomnia because they preserve sleep architecture better than BZDs. * **Inverse agonists** are primarily used in research to study the GABA-A receptor complex and are not used clinically due to their convulsant properties.

Q: Which of the following is a known side effect of ketamine?

Hallucination. **Explanation:** **Ketamine** is a unique intravenous anesthetic agent that acts as a non-competitive antagonist at **NMDA receptors**. It induces a state known as **"Dissociative Anesthesia,"** where the patient appears awake (eyes open) but is unconscious and feels no pain. **Why Hallucinations are the Correct Answer:** The most characteristic side effect of ketamine is **Emergence Delirium**. During recovery, patients often experience vivid unpleasant dreams, sensory distortions, and **hallucinations**. This occurs due to the stimulation of the limbic system while cortical sensory perception is depressed. These effects are more common in adults than children and can be minimized by co-administering benzodiazepines like midazolam. **Why the Other Options are Incorrect:** * **B & C (Hypotension and Myocardial Depression):** Unlike most anesthetics (like propofol or thiopentone) which depress the heart, ketamine is a **sympathomimetic**. It inhibits the reuptake of catecholamines, leading to **increased heart rate, cardiac output, and blood pressure**. This makes it the induction agent of choice in patients with hypovolemic shock. * **D (Decrease in ICP):** Ketamine is a potent cerebral vasodilator. It **increases cerebral blood flow and intracranial pressure (ICP)**. Therefore, it is traditionally contraindicated in patients with head injuries or intracranial space-occupying lesions. **High-Yield Clinical Pearls for NEET-PG:** * **Drug of Choice:** For induction in asthmatics (due to its potent **bronchodilatory** effect) and in patients with compensated shock. * **Reflexes:** Pharyngeal and laryngeal reflexes are usually maintained. * **Secretions:** It increases salivation (sialagogue effect); pretreatment with atropine or glycopyrrolate is often required. * **Analgesia:** Provides profound analgesia even at sub-anesthetic doses.

Q: Which of the following is a long-acting barbiturate?

Phenobarbitone. **Explanation:** Barbiturates are classified based on their **duration of action**, which is primarily determined by their lipid solubility and metabolic rate [2]. **1. Why Phenobarbitone is Correct:** **Phenobarbitone** is a classic **long-acting barbiturate** with a duration of action typically exceeding 10–12 hours (half-life of 50–120 hours). It has low lipid solubility, meaning it enters the brain slowly and remains in the systemic circulation for a longer period [2]. It is primarily used as an antiepileptic (GTCS and status epilepticus) and for daytime sedation [1]. **2. Analysis of Incorrect Options:** * **Thiopentone (Option A):** This is an **ultra-short-acting** barbiturate. Due to its extremely high lipid solubility, it crosses the blood-brain barrier almost instantly, making it ideal for the induction of anesthesia. Its action is terminated rapidly by **redistribution** from the brain to skeletal muscle and fat [2]. * **Secobarbitone (Option B) & Pentobarbitone (Option D):** These are classified as **short-to-intermediate-acting** barbiturates (duration 3–8 hours). They are more lipid-soluble than phenobarbitone and are historically used as hypnotics or for preoperative sedation. **3. High-Yield Clinical Pearls for NEET-PG:** * **Mechanism:** Barbiturates increase the **duration** of GABA-A chloride channel opening (unlike benzodiazepines, which increase frequency) [1]. * **Metabolism:** They are potent **inducers of Cytochrome P450 enzymes**, leading to numerous drug interactions (e.g., decreasing the efficacy of Warfarin or Oral Contraceptives) [3]. * **Contraindication:** Absolutely contraindicated in **Acute Intermittent Porphyria** as they induce ALA synthase. * **Excretion:** Phenobarbitone is a weak acid; its excretion can be enhanced by **alkalinization of urine** with Sodium Bicarbonate in cases of toxicity [3].

Q: Which CB1 antagonist is used in smoking cessation?

Rimonabant. **Explanation:** **Correct Answer: B. Rimonabant** Rimonabant is a selective **CB1 receptor antagonist** (inverse agonist) located in the endocannabinoid system. The endocannabinoid system plays a crucial role in regulating energy balance and the reward pathways associated with nicotine and food. By blocking CB1 receptors in the brain, Rimonabant reduces the dopamine release in the nucleus accumbens triggered by nicotine, thereby decreasing the craving for smoking. It was also used for weight loss due to its effect on appetite suppression. **Analysis of Incorrect Options:** * **A. Naloxone:** This is a competitive **opioid receptor antagonist** used primarily for the emergency reversal of opioid overdose. It has no significant role in smoking cessation. * **C. Varenicline:** This is a **partial agonist at α4β2 nicotinic acetylcholine receptors**. While it is a first-line drug for smoking cessation, its mechanism involves nicotinic receptors, not CB1 receptors. * **D. Bupropion:** This is an atypical antidepressant that acts as a **Norepinephrine-Dopamine Reuptake Inhibitor (NDRI)**. It is used in smoking cessation to reduce withdrawal symptoms but does not act on cannabinoid receptors. **High-Yield Clinical Pearls for NEET-PG:** * **The "Rimonabant Withdrawal":** Although effective for smoking cessation and obesity, Rimonabant was withdrawn from the global market due to serious **psychiatric side effects**, including severe depression, anxiety, and increased suicidal ideation. * **CB1 vs. CB2:** CB1 receptors are primarily central (CNS), while CB2 receptors are primarily peripheral (immune cells). * **First-line Smoking Cessation:** Currently, Varenicline, Bupropion, and Nicotine Replacement Therapy (NRT) are the preferred agents.

Q: Which of the following local anesthetics has the lowest intrinsic potency?

Procaine. **Explanation:** The **intrinsic potency** of a local anesthetic (LA) is primarily determined by its **lipid solubility**. Since the neuronal membrane consists of a phospholipid bilayer, drugs with higher lipid solubility can penetrate the membrane more easily to reach the sodium channel binding sites, thus requiring a lower concentration to achieve a block. **Why Procaine is correct:** Procaine is an ester-linked local anesthetic with very low lipid solubility. It is considered the **standard reference (potency = 1)** against which other LAs are measured. Due to its low lipid solubility and rapid hydrolysis by plasma pseudocholinesterase, it has the lowest intrinsic potency and the shortest duration of action among the options provided. **Analysis of Incorrect Options:** * **Lidocaine:** An amide-linked LA with intermediate lipid solubility. It is significantly more potent than procaine (Potency ≈ 2-3). * **Prilocaine:** Also an amide with intermediate potency, similar to lidocaine. It is notably associated with methemoglobinemia at high doses. * **Tetracaine:** An ester-linked LA but with very high lipid solubility. It is one of the most potent local anesthetics (Potency ≈ 8-10), often used for spinal anesthesia. **NEET-PG High-Yield Pearls:** 1. **Potency ∝ Lipid Solubility:** Determined by the aromatic ring. 2. **Duration of Action ∝ Protein Binding:** Determined by the affinity for plasma proteins (e.g., Bupivacaine has high protein binding and long duration). 3. **Onset of Action ∝ pKa:** The closer the pKa is to physiological pH (7.4), the faster the onset (Exception: Chloroprocaine). 4. **Order of Potency (Low to High):** Procaine < Lidocaine < Bupivacaine < Tetracaine.

Q: Which of the following agents does not bind to GABA receptor chloride channels?

Buspirone. ### Explanation The **GABA-A receptor** is a ligand-gated chloride channel. Several classes of drugs act as positive allosteric modulators by binding to specific sites on this receptor complex to increase chloride conductance, leading to hyperpolarization and CNS depression. **Why Buspirone is the Correct Answer:** **Buspirone** is a non-benzodiazepine anxiolytic that does **not** act on the GABA system. Its mechanism of action involves acting as a **selective partial agonist at the 5-HT1A (Serotonin) receptor**. It lacks sedative, hypnotic, anticonvulsant, and muscle relaxant properties, making it unique among anxiolytics. **Analysis of Incorrect Options:** * **Ethanol (A):** Alcohol facilitates GABA-A receptor-mediated chloride currents by binding to a specific transmembrane site, contributing to its sedative-hypnotic effects. * **Alphaxolone (B):** This is a synthetic neurosteroid used in anesthesia. Neurosteroids bind to a distinct site on the GABA-A receptor (different from the benzodiazepine site) to enhance chloride channel opening. * **Zolpidem (C):** A "Z-drug" (non-benzodiazepine sedative), it binds selectively to the **α1 subunit** of the GABA-A receptor (BZ1 site). **High-Yield Clinical Pearls for NEET-PG:** 1. **Buspirone Lag Time:** Unlike benzodiazepines, Buspirone takes **2–4 weeks** to show therapeutic effects; it is used for Generalized Anxiety Disorder (GAD) but not for acute anxiety or panic attacks. 2. **No Abuse Potential:** Buspirone does not cause physical dependence or withdrawal symptoms and does not potentiate the effects of alcohol. 3. **GABA-A vs. GABA-B:** Remember that GABA-A is ionotropic (Chloride channel), while GABA-B is metabotropic (G-protein coupled, linked to Potassium channels). **Baclofen** is the prototype GABA-B agonist.

Q: Which local anesthetic agent has antimuscarinic action on heart muscle receptors?

Cocaine. **Explanation:** **Cocaine** is unique among local anesthetics because of its complex sympathomimetic and parasympatholytic properties. While most local anesthetics are vasodilators and can cause bradycardia at high doses, cocaine is a potent vasoconstrictor and causes tachycardia. It exerts an **antimuscarinic (atropine-like) action** on the heart muscle receptors, which blocks the inhibitory effects of the vagus nerve. Additionally, it inhibits the reuptake of norepinephrine (Uptake-1) at sympathetic nerve endings. The combination of these two mechanisms leads to significant tachycardia, hypertension, and potential arrhythmias. **Analysis of Incorrect Options:** * **Procaine:** An ester-linked local anesthetic with a short duration of action. It lacks antimuscarinic properties and typically causes mild vasodilation. * **Chloroprocaine:** A halogenated derivative of procaine known for its rapid onset and low systemic toxicity due to fast metabolism by plasma cholinesterase. It does not possess antimuscarinic activity. **High-Yield Clinical Pearls for NEET-PG:** * **Vasoconstriction:** Cocaine is the **only** local anesthetic that naturally causes vasoconstriction (all others, except perhaps ropivacaine/levobupivacaine at low doses, are vasodilators). * **Metabolism:** Like other esters, cocaine is metabolized by **plasma pseudocholinesterase**. * **Toxicity:** Cocaine overdose is managed with benzodiazepines; **pure beta-blockers are contraindicated** due to the risk of "unopposed alpha-stimulation," which can lead to severe hypertension and coronary vasospasm. * **Surface Anesthesia:** Cocaine is primarily used in ENT surgeries for its excellent topical anesthesia and shrinking of mucous membranes.

Question 1

Which local anesthetic agent causes cutaneous vasoconstriction?

Accepted Answer

Ropivacaine

Answer

Lidocaine

Answer

Mepivacaine

Answer

Procaine

Question 2

A very potent and short-acting benzodiazepine was given to a patient for the purpose of causing hypnosis, but the drug caused psychiatric disturbances. Which of the following could be the hypnotic used?

Accepted Answer

Triazolam

Answer

Flurazepam

Answer

Nitrazepam

Answer

Temazepam

Question 3

The antiepileptic drug lacosamide acts by:

Accepted Answer

Inhibiting CRMP protein

Answer

Inhibiting synaptic vesicular protein

Answer

Inhibiting GABA metabolism

Answer

Inhibiting glutamate release

Question 4

Which drug has inverse agonist activity at benzodiazepine receptors?

Accepted Answer

Beta carboline

Answer

Flumazenil

Answer

Naltrexone

Answer

Zopiclone

Question 5

Which of the following is a known side effect of ketamine?

Accepted Answer

Hallucination

Answer

Hypotension

Answer

Myocardial depression

Answer

Decrease in intracranial pressure

Question 6

Which of the following is a long-acting barbiturate?

Accepted Answer

Phenobarbitone

Answer

Thiopentone

Answer

Secobarbitone

Answer

Pentobarbitone

Question 7

Which CB1 antagonist is used in smoking cessation?

Accepted Answer

Rimonabant

Answer

Naloxona

Answer

Varenicline

Answer

Bupropion

Question 8

Which of the following local anesthetics has the lowest intrinsic potency?

Accepted Answer

Procaine

Answer

Lidocaine

Answer

Prilocaine

Answer

Tetracaine

Question 9

Which of the following agents does not bind to GABA receptor chloride channels?

Accepted Answer

Buspirone

Answer

Ethanol

Answer

Alphaxolone

Answer

Zolpidem

Question 10

Which local anesthetic agent has antimuscarinic action on heart muscle receptors?

Accepted Answer

Cocaine

Answer

Procaine

Answer

Chloroprocaine

Answer

None of the above

Central Nervous System Pharmacology — MCQs

Central Nervous System Pharmacology — MCQs

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