Central Nervous System Pharmacology — MCQs

Central Nervous System Pharmacology Indian Medical PG Practice Questions and MCQs

Question 361: Which of the following benzodiazepines is considered comparatively safe in pregnancy?

A. Alprazolam
B. Zolpidem
C. Lorazepam (Correct Answer)
D. None of the above

Explanation: Benzodiazepines (BZDs) are generally avoided during pregnancy as they cross the placenta [2] and are associated with risks like "floppy infant syndrome" and neonatal withdrawal [1]. However, when pharmacological intervention is necessary, **Lorazepam** is considered the preferred choice among BZDs. **Why Lorazepam is the correct answer:** Lorazepam belongs to the **LOT** group (Lorazepam, Oxazepam, Temazepam). These drugs are metabolized solely via **Phase II glucuronidation** and do not have active metabolites. This metabolic pathway is less affected by physiological changes in pregnancy compared to Phase I oxidation. Lorazepam has a relatively shorter half-life and lower lipid solubility compared to Diazepam, reducing the risk of significant fetal accumulation. **Analysis of Incorrect Options:** * **Alprazolam:** It is a triazolobenzodiazepine associated with a higher risk of specific teratogenic effects (like cleft lip/palate) if used in the first trimester [3]. It undergoes Phase I metabolism, which can be unpredictable during pregnancy. * **Zolpidem:** While often used for insomnia, Zolpidem is a non-benzodiazepine hypnotic (Z-drug). Although some studies suggest safety, it is not the "standard" BZD answer for this clinical comparison [3]. * **None of the above:** Incorrect, as Lorazepam is clinically recognized as the safest BZD profile in this context. **NEET-PG High-Yield Pearls:** * **Teratogenicity:** BZDs are traditionally Category D [3]. First-trimester use is linked to **cleft lip and palate** [3]. * **Floppy Infant Syndrome:** Characterized by hypotonia, hypothermia, and respiratory depression in neonates born to mothers taking high-dose BZDs near term [1]. * **Metabolism Tip:** Remember **LOT** (Lorazepam, Oxazepam, Temazepam) for patients with liver dysfunction or pregnancy, as they bypass Phase I (CYP450) metabolism.

Question 362: A compound X decreases the functional activities of several CNS neurotransmitters including dopamine, adrenaline, and serotonin. At high doses, it may cause Parkinsonism-like extrapyramidal system dysfunction. Which of the following can be X?

A. Baclofen
B. Diazepam
C. Ketamine
D. Reserpine (Correct Answer)

Explanation: **Explanation:** The correct answer is **Reserpine**. **Mechanism of Action:** Reserpine is an alkaloid that irreversibly blocks the **Vesicular Monoamine Transporter (VMAT-2)**. This transporter is responsible for pumping monoamines (Dopamine, Noradrenaline, and Serotonin) from the cytoplasm into synaptic vesicles. By blocking VMAT, these neurotransmitters remain in the cytoplasm where they are degraded by the enzyme Monoamine Oxidase (MAO). This leads to a profound **depletion** of monoamine stores in both the central and peripheral nervous systems. **Clinical Correlation:** * **Parkinsonism:** Since Reserpine depletes Dopamine in the nigrostriatal pathway, it can induce drug-induced Parkinsonism (extrapyramidal symptoms). * **Depression:** Depletion of Serotonin and Noradrenaline often leads to severe secondary depression, which is a classic side effect. **Analysis of Incorrect Options:** * **A. Baclofen:** A GABA-B agonist used as a centrally acting muscle relaxant. It does not deplete monoamines. * **B. Diazepam:** A Benzodiazepine that acts as a GABA-A facilitator. It increases the frequency of chloride channel opening but does not affect monoamine storage. * **C. Ketamine:** An NMDA receptor antagonist used as a dissociative anesthetic. It typically increases sympathetic outflow rather than depleting it. **High-Yield Clinical Pearls for NEET-PG:** * **VMAT-1 vs VMAT-2:** Reserpine inhibits both, but VMAT-2 is the primary isoform in the CNS. * **Historical Use:** Formerly used as an antihypertensive and antipsychotic, but now largely obsolete due to CNS side effects. * **Key Side Effects:** Depression (suicidal ideation), Parkinsonism, hyperprolactinemia, and increased gastric acid secretion (peptic ulcers). * **Tetrabenazine:** A related drug that also inhibits VMAT-2 but is reversible; it is used to treat Huntington’s Chorea.

Question 363: Which of the following drugs is used for the prophylaxis of migraine?

A. Diclofenac
B. Flunarizine (Correct Answer)
C. Sumatriptan
D. Dihydroergotamine

Explanation: **Explanation:** The management of migraine is divided into two categories: **Abortive (Acute) therapy** and **Prophylactic (Preventive) therapy**. **Flunarizine (Option B)** is the correct answer because it is a long-acting **calcium channel blocker** specifically used for the prophylaxis of migraine. It works by preventing intracellular calcium overload and has additional antihistaminic and dopamine-antagonizing properties. Prophylaxis is indicated if a patient experiences more than 2-3 attacks per month or if the attacks are severe enough to significantly impair life. **Analysis of Incorrect Options:** * **Diclofenac (Option A):** An NSAID used for the **acute symptomatic relief** of mild-to-moderate migraine attacks. It inhibits prostaglandin synthesis but does not prevent future attacks. * **Sumatriptan (Option C):** A 5-HT$_{1B/1D}$ receptor agonist. It is the **drug of choice for acute severe migraine** attacks. It causes vasoconstriction of dilated cranial vessels but is never used for prophylaxis. * **Dihydroergotamine (Option D):** An ergot alkaloid used for the **acute treatment** of moderate-to-severe migraine. Due to its potent vasoconstrictive side effects and risk of "ergotism," it is generally reserved for patients who do not respond to triptans. **High-Yield NEET-PG Pearls:** * **First-line prophylactic drugs:** Beta-blockers (Propranolol is the most common), Amitriptyline (TCA), and Topiramate/Valproate (Anticonvulsants). * **Flunarizine** is often preferred in patients with co-existing vertigo but should be avoided in patients with a history of depression or Parkinsonism (due to risk of extrapyramidal symptoms). * **Newer Prophylactic Agents:** CGRP antagonists (e.g., Erenumab, Galcanezumab) are high-yield "monoclonal antibody" targets for refractory cases.

Question 364: A patient is diagnosed with migraine headaches and prescribed sumatriptan. What is the mechanism of action of this drug?

A. Dopamine 1 agonist
B. GABAB antagonist
C. Serotonin 1D agonist (Correct Answer)
D. Non-selective beta antagonist

Explanation: **Explanation:** **1. Why Option C is Correct:** Sumatriptan belongs to the **Triptan** class of drugs, which are the first-line agents for acute attacks of moderate-to-severe migraine. Their mechanism of action involves selective agonism at **5-HT$_{1B}$ and 5-HT$_{1D}$ receptors**. * **5-HT$_{1D}$ Agonism:** These receptors are located on the presynaptic terminals of the trigeminal nerve. Activation inhibits the release of pro-inflammatory neuropeptides (like CGRP and Substance P), preventing neurogenic inflammation. * **5-HT$_{1B}$ Agonism:** These receptors are located on cranial blood vessels. Activation leads to direct vasoconstriction of dilated intracranial extracerebral vessels, reversing the vasodilation associated with migraine pain. **2. Why Other Options are Incorrect:** * **Option A (D1 Agonist):** Dopamine agonists (like Fenoldopam) are used in hypertensive emergencies, not migraines. In fact, dopamine *antagonists* (like Metoclopramide) are used as adjuncts in migraine to treat nausea and improve gastric emptying. * **Option B (GABA$_B$ Antagonist):** GABA$_B$ *agonists* (like Baclofen) are used as muscle relaxants. Antagonists have no role in migraine therapy. * **Option D (Non-selective Beta Antagonist):** Propranolol is a non-selective beta-blocker used for migraine **prophylaxis**, not for acute treatment. It does not act as an agonist at serotonin receptors. **3. NEET-PG High-Yield Pearls:** * **Route of Administration:** Sumatriptan has low oral bioavailability (approx. 15%); subcutaneous administration is the fastest and most effective route. * **Contraindications:** Due to their vasoconstrictive properties, triptans are strictly contraindicated in patients with **Ischemic Heart Disease (IHD)**, Prinzmetal angina, or uncontrolled hypertension. * **Drug Interaction:** They should not be used within 2 weeks of MAO inhibitors or within 24 hours of Ergotamine (risk of additive vasospasm).

Question 365: Which of the following drugs is a hallucinogen?

A. Quinidine
B. Disulfiram
C. Cocaine (Correct Answer)
D. Steroids

Explanation: **Explanation:** **Correct Answer: C. Cocaine** Cocaine is a potent sympathomimetic and CNS stimulant that acts by inhibiting the reuptake of dopamine, norepinephrine, and serotonin. While primarily classified as a stimulant, high doses or chronic use can lead to **"Cocaine Psychosis,"** characterized by vivid hallucinations (visual, auditory, and tactile). A classic high-yield tactile hallucination associated with cocaine is **Formication** (Cocaine bugs/Magnan’s symptom), where the patient feels insects crawling under their skin. **Analysis of Incorrect Options:** * **A. Quinidine:** A Class IA antiarrhythmic drug. Its primary side effect profile includes "Cinchonism" (tinnitus, headache, dizziness) and QT interval prolongation, but it is not a hallucinogen. * **B. Disulfiram:** Used in alcohol aversion therapy, it inhibits aldehyde dehydrogenase. It causes the "Disulfiram-ethanol reaction" (flushing, tachycardia, nausea) when alcohol is consumed, but does not inherently cause hallucinations. * **D. Steroids:** While corticosteroids can cause "Steroid Psychosis" (mood swings, mania, or depression), they are classified as hormones/anti-inflammatory agents, not as primary hallucinogens. **NEET-PG High-Yield Pearls:** * **True Hallucinogens:** LSD (Lysergic acid diethylamide) is the most potent, acting on 5-HT2A receptors. Others include Psilocybin, Mescaline, and Phencyclidine (PCP). * **PCP (Angel Dust):** Often tested for causing vertical/rotary nystagmus and aggressive behavior. * **Formication:** Also seen in alcohol withdrawal (Delirium Tremens). * **Cocaine Treatment:** Benzodiazepines are the first-line treatment for cocaine toxicity; **Beta-blockers are contraindicated** due to the risk of unopposed alpha-adrenergic stimulation.

Question 366: Which of the following is a weak skeletal muscle relaxant?

A. Atracurium
B. Rocuronium
C. Suxamethonium (Correct Answer)
D. Rapacuronium

Explanation: **Explanation:** The classification of skeletal muscle relaxants is based on their mechanism of action and chemical structure. Muscle relaxants are categorized into **Neuromuscular Blockers (NMBs)** and **Centrally Acting Relaxants**. **Why Suxamethonium is the correct answer:** Suxamethonium (Succinylcholine) is a **depolarizing neuromuscular blocker**. Structurally, it consists of two molecules of acetylcholine joined together [1]. While it is a potent and rapid-acting agent used for endotracheal intubation, it is pharmacologically considered a **"weak"** relaxant in terms of its binding affinity and the nature of the block it produces (Phase I block) [1]. In the context of competitive potency compared to non-depolarizing agents, it is often distinguished from the "potent" competitive antagonists; for example, its potency relative to tubocurarine is approximately 0.4, making it quantitatively weaker than most non-depolarizing agents [1]. **Analysis of Incorrect Options:** * **Atracurium:** A benzylisoquinolinium non-depolarizing blocker [1]. It is a potent agent notable for undergoing **Hofmann elimination** (spontaneous degradation), making it safe in renal or hepatic failure [1]. * **Rocuronium:** An aminosteroid non-depolarizing blocker. It is a potent agent with a rapid onset, often used as an alternative to Suxamethonium for rapid sequence induction [1]. * **Rapacuronium:** Another aminosteroid non-depolarizing blocker. It was designed to be a potent, rapid-acting agent but was withdrawn from the market due to the risk of severe bronchospasm. **NEET-PG High-Yield Pearls:** * **Suxamethonium** is the drug of choice for **Rapid Sequence Induction (RSI)** due to its fastest onset and shortest duration [1]. * **Side effects of Suxamethonium:** Muscle fasciculations, hyperkalemia (avoid in burn/trauma patients), and it is a known trigger for **Malignant Hyperthermia** (Treatment: Dantrolene). * It is metabolized by **Pseudocholinesterase** (Plasma cholinesterase) [1]. Deficiency of this enzyme leads to prolonged apnea.

Question 367: Pure opiate antagonists include all of the following except:

A. Naloxone
B. Nalorphine (Correct Answer)
C. Nalmefene
D. Naltrexone

Explanation: ### Explanation The classification of opioid ligands is based on their intrinsic activity at opioid receptors (primarily $\mu$, $\kappa$, and $\delta$). **1. Why Nalorphine is the Correct Answer:** Nalorphine is a **mixed agonist-antagonist**, not a pure antagonist. It acts as a competitive antagonist at $\mu$ receptors (reversing morphine-induced respiratory depression) but behaves as a partial agonist at $\kappa$ receptors. Because it possesses intrinsic agonistic activity, it can induce dysphoria and mild analgesia, disqualifying it from being a "pure" antagonist. **2. Analysis of Incorrect Options (Pure Antagonists):** Pure antagonists have affinity for opioid receptors but zero intrinsic activity; they block the effects of both endogenous and exogenous opioids without producing any morphine-like effects. * **Naloxone:** The prototype pure antagonist. It is short-acting and administered parenterally for the acute reversal of opioid overdose. * **Naltrexone:** A long-acting pure antagonist with high oral bioavailability. It is primarily used for the maintenance of opioid-free states in addicts and for reducing alcohol cravings. * **Nalmefene:** A newer pure antagonist similar to naltrexone but with a longer half-life, used for treating opioid overdose and alcohol dependence. **3. NEET-PG High-Yield Clinical Pearls:** * **Naloxone** is the drug of choice for **Opioid Overdose** (Triad: Pinpoint pupil, Respiratory depression, Coma). * **Naltrexone** is FDA-approved for **Alcohol Dependence** (decreases the "reward" of drinking). * **Methylnaltrexone/Alvimopan:** These are peripheral $\mu$-antagonists used for **Opioid-Induced Constipation** (OIC) as they do not cross the blood-brain barrier. * **Nalorphine** is rarely used clinically today because its $\kappa$-agonism causes unpleasant side effects like hallucinations and anxiety.

Question 368: Which antiepileptic drug can lead to gingival hyperplasia?

A. Phenytoin (Correct Answer)
B. Carbamazepine
C. Valproate
D. Lamotrigine

Explanation: **Explanation:** **Phenytoin** is the correct answer. Gingival hyperplasia (overgrowth of the gums) is a classic, dose-independent side effect seen in approximately 50% of patients on long-term Phenytoin therapy. **Mechanism:** Phenytoin induces the proliferation of keratinocytes and fibroblasts. It also decreases the degradation of connective tissue by reducing the activity of collagenases and increasing the expression of Platelet-Derived Growth Factor (PDGF). This leads to an accumulation of extracellular matrix in the gingival tissues. Good oral hygiene can mitigate, but not always prevent, this condition. **Analysis of Incorrect Options:** * **B. Carbamazepine:** Primarily associated with diplopia, ataxia, and idiosyncratic reactions like SIADH (hyponatremia) and Stevens-Johnson Syndrome (SJS), especially in patients with the HLA-B*1502 allele. * **C. Valproate:** Common side effects include weight gain, alopecia (thinning of hair), hepatotoxicity, and pancreatitis. It is a known teratogen (neural tube defects). * **D. Lamotrigine:** Its most significant life-threatening side effect is a severe skin rash, which can progress to Stevens-Johnson Syndrome (SJS) or Toxic Epidermal Necrolysis (TEN). **High-Yield Clinical Pearls for NEET-PG:** * **Mnemonic for Phenytoin Side Effects (P-H-E-N-Y-T-O-I-N):** **P**-450 induction, **H**irsutism, **E**nlarged gums (Gingival Hyperplasia), **N**ystagmus, **Y**ellow-brown skin (pigmentation), **T**eratogenicity (Fetal Hydantoin Syndrome), **O**steomalacia (due to Vit D interference), **I**nterference with B12/Folate (Megaloblastic anemia), **N**europathy (Peripheral). * **Zero-order kinetics:** Phenytoin follows saturation kinetics at therapeutic concentrations, making its plasma levels unpredictable. * **Other drugs causing Gingival Hyperplasia:** Cyclosporine (immunosuppressant) and Nifedipine (Calcium Channel Blocker).

Question 369: Which one of the following is not a useful drug for the initial management of status epilepticus?

A. IV phenytoin
B. IV clobazam (Correct Answer)
C. IV thiopental
D. IV sodium valproate

Explanation: **Explanation:** **Status Epilepticus (SE)** is a medical emergency defined as continuous seizure activity lasting more than 5 minutes or recurrent seizures without recovery of consciousness. The goal of initial management is rapid termination of electrical activity. **Why IV Clobazam is the correct answer:** While Clobazam is a benzodiazepine, it is primarily used as an **adjunctive oral therapy** for Lennox-Gastaut syndrome or refractory epilepsy. It is not available in an intravenous formulation for acute emergency use in most clinical settings and lacks the rapid-onset pharmacokinetics required for the "initial" management of SE. In the emergency protocol, the preferred benzodiazepines are **IV Lorazepam** (drug of choice), **IV Diazepam**, or **IM Midazolam**. **Analysis of Incorrect Options:** * **IV Phenytoin:** This is a standard second-line agent (after benzodiazepines) used to prevent the recurrence of seizures. It provides long-term stabilization of neuronal membranes. * **IV Thiopental:** This is a potent barbiturate used in **refractory status epilepticus** (when first and second-line drugs fail). It requires ICU monitoring and intubation due to its ability to induce deep sedation and respiratory depression. * **IV Sodium Valproate:** This is an effective second-line alternative to phenytoin, especially useful in patients with generalized or myoclonic seizures, as it has a broad spectrum of activity and a better safety profile regarding cardiac arrhythmias. **High-Yield Clinical Pearls for NEET-PG:** * **Drug of Choice (Initial):** IV Lorazepam (0.1 mg/kg). It is preferred over Diazepam due to its longer duration of action in the brain. * **Pre-hospital setting:** IM Midazolam is the preferred choice if IV access is not established. * **Refractory SE:** Defined as failure of a benzodiazepine plus one second-line agent. Managed with IV Midazolam infusion, Propofol, or Thiopental. * **Fosphenytoin** is preferred over Phenytoin because it is water-soluble, causes less phlebitis ("Purple Glove Syndrome"), and can be infused faster.

Question 370: Modafinil is used as an adjunct in the treatment of which condition?

A. Sleep apnea syndrome (Correct Answer)
B. Narcolepsy
C. Attention Deficit Hyperactivity Disorder (ADHD)
D. Shift work disorder

Explanation: **Explanation:** **Modafinil** is a non-amphetamine psychostimulant that promotes wakefulness. While it is a first-line treatment for Narcolepsy, the question asks for its use as an **adjunct**. **Why Option A is Correct:** In **Obstructive Sleep Apnea (OSA)**, the primary treatment is Continuous Positive Airway Pressure (CPAP). However, many patients continue to experience residual Excessive Daytime Sleepiness (EDS) despite effective CPAP therapy. Modafinil is FDA-approved and clinically used as an **adjunct** to CPAP to manage this persistent sleepiness. It does not treat the underlying airway obstruction but improves the patient's functional wakefulness. **Analysis of Incorrect Options:** * **B. Narcolepsy:** Modafinil is considered a **first-line monotherapy** (not typically labeled as an adjunct) for EDS associated with narcolepsy due to its lower abuse potential compared to amphetamines. * **C. ADHD:** While sometimes used "off-label" in adults who do not respond to stimulants, it is not a standard or primary adjunct treatment for ADHD. * **D. Shift Work Disorder:** Modafinil is a **primary treatment** indicated for patients with Shift Work Sleep Disorder to improve alertness during work hours; it is not used adjunctively here. **High-Yield Clinical Pearls for NEET-PG:** * **Mechanism of Action:** It inhibits the reuptake of Dopamine (DAT inhibitor) and increases levels of **Orexin/Hypocretin** and Histamine in the hypothalamus. * **Side Effects:** Most common is headache. Serious but rare: **Stevens-Johnson Syndrome (SJS)**. * **Advantage:** Unlike amphetamines, it has low peripheral sympathomimetic activity (less tachycardia/hypertension) and lower potential for addiction. * **Armodafinil:** The R-enantiomer of modafinil with a longer half-life.

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

Practice Questions

Drugs of Abuse and Addiction

Practice Questions

Psychostimulants

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Hallucinogens

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CNS Stimulants and Cognitive Enhancers

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