Central Nervous System Pharmacology — MCQs

Central Nervous System Pharmacology Indian Medical PG Practice Questions and MCQs

Question 521: Which of the following is an increased risk associated with Risperidone use?

A. Cerebrovascular accidents (Correct Answer)
B. Extrapyramidal symptoms
C. Agranulocytosis
D. Diabetes insipidus

Explanation: **Explanation:** **Risperidone** is a second-generation (atypical) antipsychotic. While all atypical antipsychotics carry a "Black Box Warning" regarding increased mortality in elderly patients with dementia-related psychosis, **Risperidone** specifically has a well-documented association with an increased risk of **Cerebrovascular Accidents (CVAs)**, such as strokes and transient ischemic attacks (TIAs), in this vulnerable population. The underlying mechanism is thought to involve a combination of orthostatic hypotension, thromboembolic effects, and altered cardiovascular reflex sensitivity. **Analysis of Incorrect Options:** * **B. Extrapyramidal Symptoms (EPS):** While Risperidone can cause EPS (especially at doses >6mg), it is an *atypical* antipsychotic designed to have a *lower* risk of EPS compared to first-generation drugs like Haloperidol. Therefore, CVA is the more specific "increased risk" highlighted in clinical warnings for this class in the elderly. * **C. Agranulocytosis:** This is a classic, life-threatening side effect specifically associated with **Clozapine**, requiring mandatory WBC monitoring. It is not a characteristic risk of Risperidone. * **D. Diabetes Insipidus:** Nephrogenic Diabetes Insipidus is a hallmark side effect of **Lithium** therapy, not antipsychotics. **High-Yield Clinical Pearls for NEET-PG:** * **Hyperprolactinemia:** Among atypical antipsychotics, Risperidone has the highest propensity to increase prolactin levels (causing gynecomastia/amenorrhea). * **Metabolic Syndrome:** Atypical antipsychotics (especially Clozapine and Olanzapine) are high-risk for weight gain, dyslipidemia, and Type 2 Diabetes. * **Active Metabolite:** The active metabolite of Risperidone is **Paliperidone**, which is available as a long-acting injectable.

Question 522: All of the following are Glutamate receptors except?

A. Kainate receptors
B. NMDA receptors
C. AMDA receptors (Correct Answer)
D. AMPA receptors

Explanation: **Explanation:**Glutamate is the primary excitatory neurotransmitter in the Central Nervous System (CNS) [2]. Its receptors are broadly classified into two categories: **Ionotropic** (ligand-gated ion channels) and **Metabotropic** (G-protein coupled receptors) [1, 2].1. **Why Option C is Correct:** **AMDA receptors** do not exist in medical pharmacology. This is a distractor term often confused with AMPA. The correct acronyms for ionotropic glutamate receptors are NMDA, AMPA, and Kainate [1, 2].2. **Analysis of Incorrect Options:** * **AMPA (α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid):** These are ionotropic receptors responsible for fast excitatory synaptic transmission. They primarily allow the influx of $Na^+$ and efflux of $K^+$ [1, 2]. * **NMDA (N-methyl-D-aspartate):** These are unique voltage-dependent ionotropic receptors [2]. At resting membrane potential, they are blocked by **Magnesium ($Mg^{2+}$)** ions. They are highly permeable to $Ca^{2+}$ and play a crucial role in long-term potentiation (memory) [1]. * **Kainate Receptors:** These are found in the hippocampus and cerebellum; they function similarly to AMPA receptors but are less common [1, 2].**High-Yield Clinical Pearls for NEET-PG:** * **Excitotoxicity:** Excessive glutamate stimulation leads to neuronal death (seen in stroke and Alzheimer’s) due to massive $Ca^{2+}$ influx via NMDA receptors [1].* **Memantine:** An NMDA receptor antagonist used in the treatment of moderate-to-severe Alzheimer’s disease [1].* **Ketamine & Phencyclidine (PCP):** These act as non-competitive antagonists at the NMDA receptor [1].* **Ketamine** is often used as a dissociative anesthetic [1].

Question 523: All of the following statements about the treatment of migraine are true, except:

A. Narotriptan has a slower onset and longer half-life than sumatriptan.
B. Rizatriptan is more efficacious than sumatriptan.
C. Sumatriptan is a selective 5-HT 1B/1D agonist.
D. Sumatriptan is used for chronic migraine. (Correct Answer)

Explanation: **Explanation:** The correct answer is **D** because **Sumatriptan is used for the acute management of migraine attacks**, not for chronic migraine prophylaxis. **1. Why Option D is the correct (incorrect statement):** In pharmacology, migraine treatment is divided into **Abortive (Acute)** and **Prophylactic (Chronic)** therapy. Sumatriptan (and other triptans) are potent vasoconstrictors used to terminate an ongoing attack. Chronic migraine (defined as ≥15 headache days/month) requires prophylactic agents like Topiramate, Propranolol, Amitriptyline, or Flunarizine to reduce frequency. Using triptans too frequently for chronic migraine can actually lead to **Medication Overuse Headache (MOH)**. **2. Analysis of other options:** * **Option A:** Narotriptan has higher oral bioavailability and a longer half-life (~6 hours) compared to Sumatriptan (~2 hours), leading to a slower onset but lower recurrence rates. * **Option B:** Rizatriptan (10mg) has been shown in clinical trials to have slightly higher efficacy and faster onset than the standard 50mg/100mg dose of Sumatriptan. * **Option C:** Triptans are selective agonists at **5-HT 1B** (causing cranial vasoconstriction) and **5-HT 1D** (inhibiting neuropeptide release from trigeminal nerves) receptors. **NEET-PG High-Yield Pearls:** * **Drug of Choice (DOC) for Acute Severe Migraine:** Sumatriptan (Subcutaneous is fastest). * **DOC for Prophylaxis:** Propranolol (Beta-blocker). * **Contraindication:** Triptans are contraindicated in patients with **Ischemic Heart Disease (IHD)** or Prinzmetal angina due to coronary vasoconstriction. * **Newer Agents:** **Lasmiditan** (5-HT 1F agonist) is used for patients with cardiovascular risks as it does not cause vasoconstriction.

Question 524: A 25-year-old woman with myoclonic seizures is well controlled on valproate. She indicates that she is interested in conceiving in the next year. With respect to her antiepileptic medication, what should be considered?

A. Leave her on current therapy
B. Switch to lamotrigine (Correct Answer)
C. Decrease valproate dose
D. None of the above

Explanation: ### Explanation **1. Why the correct answer is right:** Sodium Valproate is highly effective for generalized epilepsies (including myoclonic seizures), but it is the most **teratogenic** antiepileptic drug (AED). It is associated with a high risk of **neural tube defects** (e.g., spina bifida), craniofacial abnormalities, and impaired cognitive development in the offspring. In a woman planning pregnancy, the goal is to switch to an AED with a lower teratogenic profile before conception [1]. **Lamotrigine** and Levetiracetam are considered the safest alternatives during pregnancy, as they carry the lowest risk of major congenital malformations. **2. Why the incorrect options are wrong:** * **Option A:** Continuing Valproate is contraindicated in a woman planning pregnancy unless all other options have failed, due to the significant risk of physical and neurodevelopmental defects. * **Option C:** While the risk of teratogenicity is dose-dependent (higher risk >1000 mg/day), there is no "safe" dose of Valproate that eliminates the risk. Switching to a safer drug is preferred over merely reducing the dose of a known teratogen. **3. Clinical Pearls for NEET-PG:** * **Valproate & Pregnancy:** Causes neural tube defects by interfering with folate metabolism. Supplementation with **high-dose Folic Acid (5 mg/day)** is mandatory if Valproate must be used. * **Drug of Choice (DOC):** Valproate is the DOC for myoclonic seizures in non-pregnant patients. However, in pregnancy, Lamotrigine or Levetiracetam are preferred. * **Phenytoin/Carbamazepine:** These cause **Fetal Hydantoin Syndrome** (cleft lip/palate, digital hypoplasia). * **Management Tip:** Always switch medications *before* conception to ensure seizure control is maintained on the new agent, as switching during pregnancy increases the risk of breakthrough seizures and status epilepticus.

Question 525: Which of the following serotonergic receptors functions as an autoreceptor?

A. 5-HT1a (Correct Answer)
B. 5-HT1B/1D
C. 5-HT2a
D. 5-HT

Explanation: ### Explanation **Correct Option: A (5-HT1A)** In the central nervous system, **autoreceptors** are receptors located on the presynaptic neuron that provide negative feedback, inhibiting the further release or firing of that specific neurotransmitter. * **5-HT1A** receptors function as **somatodendritic autoreceptors** primarily located in the **Raphe nuclei**. When stimulated, they decrease the firing rate of serotonergic neurons, thereby reducing the overall release of serotonin (5-HT). This is a high-yield concept in the mechanism of action of SSRIs, where chronic stimulation leads to the downregulation of these autoreceptors, eventually increasing serotonin levels in the synapse. **Analysis of Incorrect Options:** * **B. 5-HT1B/1D:** While these are also inhibitory, they are primarily **terminal autoreceptors** (located on the axon terminals) rather than somatodendritic. While technically autoreceptors, 5-HT1A is the classic "textbook" answer for somatodendritic feedback in the Raphe nuclei. (Note: 5-HT1D is the target for Triptans in migraine). * **C. 5-HT2A:** These are **postsynaptic** excitatory receptors coupled to the Gq protein. They are the primary targets for atypical antipsychotics (antagonism) and hallucinogens like LSD (agonism). * **D. 5-HT:** This is the neurotransmitter itself (Serotonin), not a specific receptor subtype. **NEET-PG High-Yield Pearls:** 1. **Buspirone:** A selective **5-HT1A partial agonist** used as a non-benzodiazepine anxiolytic (takes 2 weeks to work). 2. **All 5-HT receptors are G-protein coupled (GPCRs) EXCEPT 5-HT3**, which is a ligand-gated ion channel (target for Ondansetron). 3. **5-HT4 agonists** (e.g., Prucalopride) are used as prokinetics in chronic constipation. 4. **5-HT2C antagonism** is associated with weight gain in patients taking atypical antipsychotics like Clozapine.

Question 526: Which of the following statements regarding benzodiazepines is true?

A. Benzodiazepines act as GABA agonists.
B. Diazepam is a short-acting benzodiazepine.
C. Diazepam causes lesser respiratory depression than midazolam. (Correct Answer)
D. Nitrazepam is metabolized in the liver.

Explanation: **Explanation:** **1. Why Option C is Correct:** Benzodiazepines (BZDs) generally have a high therapeutic index and cause minimal respiratory depression when used alone. However, **Midazolam** is a potent, rapid-acting BZD often used for conscious sedation and induction. It is associated with a higher risk of dose-dependent respiratory depression and apnea compared to **Diazepam**, particularly when administered intravenously. Diazepam has a slower onset of central effect and a more predictable respiratory profile in clinical settings. **2. Analysis of Incorrect Options:** * **Option A:** BZDs are **Positive Allosteric Modulators**, not GABA agonists. They increase the *frequency* of chloride channel opening in the presence of GABA but cannot open the channel independently. * **Option B:** Diazepam is a **long-acting** BZD. It has a long elimination half-life (20–50 hours) and is converted into active metabolites like desmethyldiazepam, which further extends its duration of action (up to 100 hours). * **Option D:** While most BZDs undergo oxidative metabolism in the liver, **Nitrazepam** is primarily metabolized via **nitro-reduction**. (Note: While this occurs in the liver, in the context of NEET-PG, the distinction often lies in its specific metabolic pathway or its classification as a hypnotic). **Clinical Pearls for NEET-PG:** * **Mechanism:** BZDs increase the **frequency** of Cl⁻ channel opening; Barbiturates increase the **duration**. * **Antidote:** **Flumazenil** is a competitive BZD receptor antagonist used for overdose. * **Metabolism:** BZDs that do not form active metabolites (safe in elderly/liver failure) are **L**orazepam, **O**xazepam, and **T**emazepam (**LOT**). * **Shortest acting BZD:** Midazolam/Triazolam; **Longest acting:** Flurazepam/Diazepam.

Question 527: Which of the following is an FDA-approved indication for the adjunctive use of modafinil?

A. Major depression and associated lethargy
B. Narcolepsy
C. Obstructive sleep apnea (Correct Answer)
D. Shift work disorder

Explanation: **Explanation:** Modafinil is a non-amphetamine wakefulness-promoting agent. While it is used in all three sleep-related disorders listed (Narcolepsy, OSA, and SWD), the question asks for its role as an **adjunctive** treatment. * **Correct Option (C):** In **Obstructive Sleep Apnea (OSA)**, the primary treatment is Continuous Positive Airway Pressure (CPAP). However, some patients experience persistent excessive daytime sleepiness (EDS) despite effective CPAP therapy. Modafinil is FDA-approved specifically as an **adjunct** to CPAP to manage this residual sleepiness. * **Incorrect Options (B & D):** In **Narcolepsy** and **Shift Work Disorder (SWD)**, modafinil is typically used as a **first-line monotherapy** to improve wakefulness, rather than an adjunctive treatment to another primary intervention. * **Incorrect Option (A):** While modafinil is sometimes used "off-label" to treat fatigue or lethargy associated with **Major Depressive Disorder**, it is not an FDA-approved indication. **High-Yield Clinical Pearls for NEET-PG:** 1. **Mechanism of Action:** It inhibits the reuptake of dopamine by binding to the dopamine transporter (DAT), increasing extracellular dopamine levels in the hypothalamus. It also increases levels of **orexin/hypocretin** and histamine. 2. **Advantages:** Unlike amphetamines, it has a lower potential for abuse, less peripheral sympathetic activation (less tachycardia/hypertension), and a lower risk of rebound hypersomnia. 3. **Adverse Effects:** Most common is headache. Serious but rare: **Stevens-Johnson Syndrome (SJS)**. 4. **Drug Interactions:** It is a mild inducer of CYP3A4, which can reduce the efficacy of **oral contraceptive pills (OCPs)**.

Question 528: Rizatriptan is a drug used for?

A. Prophylaxis of migraine
B. Acute migraine (Correct Answer)
C. Cluster headache
D. Chronic migraine

Explanation: **Explanation:** **Rizatriptan** belongs to the "Triptan" class of drugs, which are **selective 5-HT$_{1B/1D}$ receptor agonists**. They are the first-line treatment for the **abortive (acute) management** of moderate-to-severe migraine attacks. **Why the correct answer is right:** Triptans work through three primary mechanisms to treat an acute attack: 1. **Vasoconstriction:** Stimulation of 5-HT$_{1B}$ receptors on intracranial blood vessels reverses the painful vasodilation. 2. **Inhibition of Neuropeptides:** Stimulation of 5-HT$_{1D}$ receptors on trigeminal nerve terminals inhibits the release of pro-inflammatory peptides (like CGRP and Substance P). 3. **Central Inhibition:** They reduce pain transmission in the trigeminal nucleus caudalis. **Why incorrect options are wrong:** * **Prophylaxis of Migraine (A):** Prophylactic drugs are used to reduce the frequency of attacks and include Beta-blockers (Propranolol), Anticonvulsants (Topiramate, Valproate), or TCAs (Amitriptyline). Triptans have a short half-life and are not used for daily prevention. * **Cluster Headache (C):** While Sumatriptan (SC/Nasal) is used for acute cluster headaches, Rizatriptan is specifically indicated and most commonly associated with migraine management in exam contexts. * **Chronic Migraine (D):** Chronic migraine (≥15 days/month) requires long-term prophylactic therapy (e.g., Botulinum toxin or CGRP antagonists) rather than just acute symptomatic relief. **High-Yield Clinical Pearls for NEET-PG:** * **Fastest Acting Oral Triptan:** Rizatriptan has the quickest onset of action among oral triptans. * **Longest Acting Triptan:** Frovatriptan (longest half-life, ~26 hours). * **Contraindications:** Due to vasoconstrictive properties, triptans are strictly contraindicated in patients with **Ischemic Heart Disease (IHD)**, Prinzmetal angina, and uncontrolled hypertension. * **Drug Interaction:** Propranolol can increase the plasma concentration of Rizatriptan; therefore, the dose of Rizatriptan should be halved (5 mg) if used concurrently.

Question 529: Which of the following antiepileptic drugs is also a free radical scavenger?

A. Levetiracetam
B. Topiramate
C. Zonisamide (Correct Answer)
D. Gabapentin

Explanation: **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.

Question 530: Which of the following statements about dezocine is true?

A. Dezocine acts slower than morphine.
B. Dezocine is less potent than morphine.
C. Dezocine acts on GABA receptors.
D. Dezocine does not increase histamine release. (Correct Answer)

Explanation: **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.

Practice by Chapter

General Anesthetics

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Local Anesthetics

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Sedative-Hypnotics

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Antiepileptic Drugs

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Antiparkinsonian Drugs

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Opioid Analgesics

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Drugs of Abuse and Addiction

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Psychostimulants

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Hallucinogens

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CNS Stimulants and Cognitive Enhancers

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