Central Nervous System Pharmacology — MCQs
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All are atypical antipsychotic drugs except?
What is the drug of choice to control convulsions in eclampsia?
Which of the following drugs can be used in opioid de-addiction?
A 22-year-old female on antiepileptic therapy got married. When should folic acid supplementation be advised to this female?
A patient on therapy for a Central Nervous System illness develops an abnormality. What is the possible cause?
What is the drug of choice for pain relief in diabetic neuropathy?
What is the drug of choice for Trigeminal neuralgia?
Which of the following drugs does not affect the GABAA receptor?
High plasma drug concentration of phenytoin can cause which of the following adverse effects?
In methyl alcohol poisoning, CNS depression, cardiac depression, and optic nerve atrophy occur. What substances produce these effects?
Central Nervous System Pharmacology Indian Medical PG Practice Questions and MCQs
Question 491: All are atypical antipsychotic drugs except?
- A. Clozapine
- B. Risperidone
- C. Olanzapine
- D. Loxapine (Correct Answer)
Explanation: **Explanation:** The classification of antipsychotics is based on their mechanism of action and side-effect profile. Antipsychotics are divided into **Typical (First Generation)** and **Atypical (Second Generation)** drugs. **Why Loxapine is the correct answer:** Loxapine is a **Typical Antipsychotic** belonging to the tricyclic subclass (dibenzoxazepine). It primarily acts by blocking **D2 receptors** in the mesolimbic and nigrostriatal pathways. Unlike atypical drugs, typical antipsychotics like Loxapine have a higher propensity to cause Extrapyramidal Side Effects (EPS) and do not significantly block 5-HT2A receptors. **Why the other options are incorrect:** * **Clozapine:** The prototype atypical antipsychotic. It is a "loose" D2 blocker with high affinity for 5-HT2A, D4, and Muscarinic receptors. It is the gold standard for treatment-resistant schizophrenia. * **Risperidone:** A potent atypical agent that blocks both D2 and 5-HT2A receptors. At higher doses (>6mg), it behaves more like a typical antipsychotic, increasing the risk of EPS and hyperprolactinemia. * **Olanzapine:** An atypical drug structurally related to clozapine. It is effective for both positive and negative symptoms but is notorious for causing significant weight gain and metabolic syndrome. **High-Yield Clinical Pearls for NEET-PG:** * **Atypical vs. Typical:** Atypicals are defined by a **high 5-HT2A:D2 blockade ratio**, lower risk of EPS, and better efficacy against negative symptoms. * **Clozapine Safety:** Requires mandatory WBC monitoring due to the risk of **agranulocytosis** (1%). It also lowers the seizure threshold. * **Loxapine Unique Fact:** While classified as typical, it is sometimes considered "atypical-like" at low doses, but for exam purposes, it remains in the Typical category. An inhaled formulation is used for acute agitation. * **Weight Gain:** Clozapine and Olanzapine cause the most weight gain; Ziprasidone and Aripiprazole cause the least.
Question 492: What is the drug of choice to control convulsions in eclampsia?
- A. Pethidine
- B. Diazepam
- C. Magnesium sulphate (Correct Answer)
- D. Phenytoin
Explanation: **Explanation:** **Magnesium Sulphate ($MgSO_4$)** is the gold standard and drug of choice for both the prevention and control of seizures in eclampsia. Its superiority over other anticonvulsants was established by the landmark **Collaborative Eclampsia Trial**. **Why it is the Correct Choice:** $MgSO_4$ acts primarily by blocking **NMDA receptors** in the brain, which raises the seizure threshold. It also acts as a potent cerebral vasodilator, reversing the vasospasm associated with eclampsia. Additionally, it inhibits acetylcholine release at the neuromuscular junction, providing a mild muscle-relaxant effect. Unlike other anticonvulsants, it effectively prevents recurrent seizures without causing significant maternal CNS depression. **Why Other Options are Incorrect:** * **Pethidine (A):** This is an opioid analgesic used for pain relief during labor. It has no anticonvulsant properties and can cause respiratory depression in the neonate. * **Diazepam (B):** While a potent benzodiazepine for status epilepticus, it is associated with a higher rate of seizure recurrence in eclampsia and can cause "Floppy Infant Syndrome" (neonatal hypotonia and respiratory depression). * **Phenytoin (C):** It is less effective than $MgSO_4$ in preventing recurrent eclamptic fits and requires slow intravenous infusion to avoid cardiac arrhythmias. **High-Yield Clinical Pearls for NEET-PG:** * **Regimens:** Pritchard (IM) and Zuspan (IV) are the standard protocols. * **Therapeutic Window:** 4–7 mEq/L. * **Monitoring:** Always check for **Patellar reflex** (earliest sign of toxicity), **Respiratory rate** (>12/min), and **Urine output** (>30 ml/hr). * **Antidote:** 10 ml of 10% **Calcium Gluconate** (IV) administered over 10 minutes.
Question 493: Which of the following drugs can be used in opioid de-addiction?
- A. Clonidine
- B. Diazepam
- C. Methadone
- D. All of the above (Correct Answer)
Explanation: **Explanation:** Opioid de-addiction involves two distinct phases: **detoxification** (managing acute withdrawal symptoms) and **maintenance therapy** (preventing relapse). The correct answer is "All of the above" because each drug targets a specific component of the withdrawal syndrome. 1. **Methadone (Option C):** This is a long-acting **μ-opioid agonist**. It is used in "Opioid Substitution Therapy" (OST). Because of its long half-life, it prevents withdrawal symptoms and reduces "drug-seeking behavior" by providing a stable plasma concentration without the intense euphoria associated with heroin. 2. **Clonidine (Option A):** Opioid withdrawal causes massive sympathetic overactivity (tachycardia, hypertension, tremors, lacrimation). Clonidine, an **$\alpha_2$ agonist**, acts centrally to decrease sympathetic outflow, effectively managing the autonomic symptoms of withdrawal. 3. **Diazepam (Option B):** Benzodiazepines are used as adjuvant therapy during detoxification to manage the severe **anxiety, agitation, and insomnia** that accompany opioid abstinence. **High-Yield Clinical Pearls for NEET-PG:** * **Gold Standard for Maintenance:** Methadone or Buprenorphine (a partial $\mu$ agonist and $\kappa$ antagonist). * **Buprenorphine + Naloxone:** This combination (Suboxone) is preferred for office-based treatment to prevent intravenous abuse of the tablet. * **Naltrexone:** An opioid antagonist used *after* detoxification to prevent relapse by blocking the effects of any opioids consumed. It must NOT be given during active withdrawal as it will precipitate a crisis. * **Ultra-rapid Detoxification:** Involves using Naloxone under anesthesia to accelerate the withdrawal process.
Question 494: A 22-year-old female on antiepileptic therapy got married. When should folic acid supplementation be advised to this female?
- A. 3 months before pregnancy
- B. All women who could become pregnant (Correct Answer)
- C. As soon as pregnancy is confirmed
- D. After delivery
Explanation: **Explanation:** The correct answer is **B. All women who could become pregnant.** **1. Why Option B is Correct:** Antiepileptic drugs (AEDs), particularly enzyme inducers (like Carbamazepine, Phenytoin) and Valproate, interfere with folate metabolism. Low folate levels are strongly associated with **Neural Tube Defects (NTDs)** like spina bifida. Since the neural tube closes by the **28th day of gestation**—often before a woman even realizes she is pregnant—supplementation must be started preemptively. For women on AEDs, the risk of malformations is 2-3 times higher than the general population; therefore, continuous supplementation is recommended for any woman of childbearing age who is sexually active. **2. Why Other Options are Incorrect:** * **Option A:** While starting 3 months prior is ideal for planned pregnancies, many pregnancies are unplanned. Waiting for a "pre-conception window" leaves many women unprotected. * **Option C:** By the time pregnancy is confirmed (usually week 5-6), the neural tube has already closed. Supplementation at this stage is too late to prevent NTDs. * **Option D:** Post-delivery supplementation does not address the teratogenic risks associated with AEDs during organogenesis. **3. High-Yield Clinical Pearls for NEET-PG:** * **Dosage:** While 0.4 mg is standard for the general population, women on AEDs are often prescribed a higher dose (**5 mg/day**) of folic acid. * **Valproate:** Carries the highest risk of NTDs and cognitive impairment; it should be avoided in women of childbearing age if alternatives exist. * **Drug of Choice:** Levetiracetam and Lamotrigine are generally considered the safest AEDs during pregnancy. * **Vitamin K:** Enzyme-inducing AEDs can cause Vitamin K deficiency in the newborn; 1 mg of Vitamin K should be administered to the neonate at birth to prevent hemorrhagic disease.
Question 495: A patient on therapy for a Central Nervous System illness develops an abnormality. What is the possible cause?
- A. Antidepressants
- B. Antipsychotics (Correct Answer)
- C. Antiepileptics
- D. Anti-Parkinsonian drugs
Explanation: ***Antipsychotics*** - **Thioridazine** and other antipsychotics are well-known to cause **retinal pigmentary changes** and **bull's eye maculopathy**, especially with prolonged use. - The **phenothiazine class** antipsychotics have particular **retinal toxicity** due to their affinity for melanin-containing tissues in the eye. *Antidepressants* - Antidepressants do **not typically cause retinopathy** or significant ocular pigmentary changes. - Common side effects include **dry mouth**, **sedation**, and **anticholinergic effects**, but not retinal abnormalities. *Antiepileptics* - **Vigabatrin** can cause **bilateral concentric visual field defects**, but this presents as **peripheral field loss** rather than bull's eye maculopathy. - Other antiepileptics like **phenytoin** cause **gingival hyperplasia** and **hirsutism**, not retinal pigmentary changes. *Anti-Parkinsonian drugs* - These medications primarily cause **dyskinesias**, **hallucinations**, and **orthostatic hypotension** but do not cause retinopathy. - **Levodopa** and **dopamine agonists** affect motor function and behavior, not retinal pigmentation.
Question 496: What is the drug of choice for pain relief in diabetic neuropathy?
- A. Gabapentin
- B. Lamotrigine
- C. Pregabalin (Correct Answer)
- D. Mexiletine
Explanation: ### Explanation **Correct Option: C. Pregabalin** Pregabalin is currently considered the **first-line drug of choice** for painful diabetic neuropathy. It is a structural analog of GABA that acts by binding to the **$\alpha_2\delta$ subunit of voltage-gated calcium channels** in the CNS. This binding decreases the influx of calcium into nerve terminals, thereby reducing the release of excitatory neurotransmitters like glutamate, substance P, and norepinephrine. It is preferred over Gabapentin due to its superior pharmacokinetic profile, including linear absorption and higher bioavailability. **Analysis of Incorrect Options:** * **A. Gabapentin:** While also a first-line agent and structurally similar to Pregabalin, it has non-linear (saturable) absorption. In clinical guidelines (e.g., ADA, AAN), Pregabalin is often cited as the drug with the strongest evidence base for initial therapy. * **B. Lamotrigine:** This is an antiepileptic that acts by blocking voltage-gated sodium channels. While used for trigeminal neuralgia or bipolar disorder, it is not a first-line agent for diabetic neuropathy. * **D. Mexiletine:** An oral Class IB antiarrhythmic (sodium channel blocker). It was historically used for neuropathic pain but is now rarely used due to its narrow therapeutic index and significant side effect profile. **High-Yield Clinical Pearls for NEET-PG:** * **FDA Approved First-line agents:** Pregabalin, Duloxetine (SNRI), and Tapentadol (Opioid). * **Mechanism:** Pregabalin/Gabapentin do **not** act on GABA receptors; they act on $\alpha_2\delta$ calcium channel subunits. * **Side Effects:** Dizziness, somnolence, and peripheral edema are common with Pregabalin. * **Tricyclic Antidepressants (TCAs):** Amitriptyline is also highly effective but often avoided in elderly patients due to anticholinergic side effects.
Question 497: What is the drug of choice for Trigeminal neuralgia?
- A. Carbamazepine (Correct Answer)
- B. Phenobarbital
- C. Phenytoin
- D. Valproic acid
Explanation: **Explanation:** **1. Why Carbamazepine is the Correct Answer:** Carbamazepine is the **Drug of Choice (DOC)** for Trigeminal Neuralgia (Tic Douloureux). Its primary mechanism of action involves the **blockade of voltage-gated sodium channels** in their inactivated state. This stabilizes neuronal membranes and inhibits the high-frequency repetitive firing of the trigeminal nerve, effectively reducing the paroxysmal stabbing pain characteristic of this condition. **2. Why Other Options are Incorrect:** * **Phenobarbital:** Primarily used for neonatal seizures and status epilepticus. It acts via GABA-A receptors and is not effective for neuropathic pain. * **Phenytoin:** While it also blocks sodium channels and was historically used for trigeminal neuralgia, it is less effective than Carbamazepine and carries a higher risk of side effects like gingival hyperplasia and hirsutism. * **Valproic Acid:** A broad-spectrum anticonvulsant used for generalized seizures and migraine prophylaxis, but it lacks specific efficacy for the lancinating pain of trigeminal neuralgia. **3. Clinical Pearls for NEET-PG:** * **Adverse Effects:** Watch for **diplopia, ataxia**, and serious skin reactions like **Stevens-Johnson Syndrome (SJS)**, especially in patients with the **HLA-B*1502** allele. * **Metabolism:** It is a potent **enzyme inducer** and exhibits **auto-induction** (it induces its own metabolism). * **Other Indications:** It is also used for Bipolar Disorder (as a mood stabilizer) and Glossopharyngeal neuralgia. * **Second-line agents:** If Carbamazepine fails or is not tolerated, **Oxcarbazepine** (better tolerated) or **Baclofen** (GABA-B agonist) are often considered.
Question 498: Which of the following drugs does not affect the GABAA receptor?
- A. Muscimol
- B. Alcohol
- C. Picrotoxin
- D. Buspirone (Correct Answer)
Explanation: **Explanation:** The **GABA$_A$ receptor** is a ligand-gated chloride channel (ionotropic receptor) that mediates fast inhibitory neurotransmission in the CNS. It features multiple binding sites for various pharmacological agents. **Why Buspirone is the Correct Answer:** **Buspirone** is a non-benzodiazepine anxiolytic that does **not** act on GABA receptors. Instead, it acts as a **selective partial agonist at the 5-HT$_{1A}$ (Serotonin) receptor**. It is used for Generalized Anxiety Disorder (GAD) and is preferred in patients where sedation or cognitive impairment must be avoided, as it lacks the sedative, anticonvulsant, and muscle relaxant properties of benzodiazepines. **Analysis of Incorrect Options:** * **Muscimol:** A potent, selective **agonist** at the GABA binding site of the GABA$_A$ receptor. It is derived from the mushroom *Amanita muscaria*. * **Alcohol (Ethanol):** Ethanol is a CNS depressant that **potentiates** the GABA$_A$ receptor by increasing the duration of chloride channel opening (similar to barbiturates). * **Picrotoxin:** A non-competitive **antagonist** that binds to the picrotoxin site within the chloride channel pore, effectively blocking chloride conductance. It is a potent convulsant. **High-Yield Clinical Pearls for NEET-PG:** * **GABA$_A$ vs. GABA$_B$:** GABA$_A$ is ionotropic (Cl⁻ channel); GABA$_B$ is metabotropic (G-protein coupled, linked to K⁺ channels). **Baclofen** is the prototype GABA$_B$ agonist. * **Benzodiazepines vs. Barbiturates:** BDZs increase the **frequency** of channel opening; Barbiturates increase the **duration** of channel opening. * **Buspirone Advantage:** It has no potential for abuse or addiction (no "withdrawal" or "tolerance") and does not interact with alcohol. However, it has a slow onset of action (takes 2–4 weeks to work).
Question 499: High plasma drug concentration of phenytoin can cause which of the following adverse effects?
- A. Ataxia (Correct Answer)
- B. Hirsutism
- C. Gum hyperplasia
- D. All of the above
Explanation: Phenytoin is a commonly prescribed antiepileptic drug with a narrow therapeutic index (10–20 µg/mL). Its adverse effects are classically categorized into **dose-dependent (toxic)** and **non-dose-dependent (chronic)** effects. ### 1. Why "Ataxia" is the Correct Answer Ataxia is a **dose-dependent** neurological side effect. As plasma concentrations of phenytoin rise above the therapeutic range (>20 µg/mL), it causes cerebellar-vestibular dysfunction. The progression of toxicity typically follows this sequence: **Nystagmus → Ataxia → Diplopia → Vertigo → Coma.** Because the question specifies "high plasma drug concentration," it refers to acute toxicity, where ataxia is a hallmark sign. ### 2. Why Other Options are Incorrect * **B. Hirsutism & C. Gum Hyperplasia:** These are **non-dose-dependent** or chronic side effects. They occur over long-term therapy regardless of whether the plasma concentration is acutely high. They are related to altered collagen metabolism and androgenic effects rather than immediate drug toxicity. * **D. All of the above:** While all three are side effects of phenytoin, only ataxia is directly correlated with a "high plasma concentration" (toxicity). ### 3. High-Yield Clinical Pearls for NEET-PG * **Kinetics:** Phenytoin follows **Zero-order kinetics** (capacity-limited elimination) at high doses. Small dose increases can lead to disproportionately large increases in plasma levels. * **Teratogenicity:** Causes **Fetal Hydantoin Syndrome** (cleft lip/palate, digital hypoplasia). * **Mnemonic (P-H-E-N-Y-T-O-I-N):** **P**-450 inducer, **H**irsutism, **E**nlarged gums, **N**ystagmus, **Y**ellow-brown skin (pigmentation), **T**eratogenicity, **O**steomalacia, **I**nterference with B12/Folate (Megaloblastic anemia), **N**europathy. * **Infusion:** Must be given in Normal Saline (precipitates in Dextrose). Fosphenytoin is the water-soluble prodrug used to avoid local complications like "Purple Glove Syndrome."
Question 500: In methyl alcohol poisoning, CNS depression, cardiac depression, and optic nerve atrophy occur. What substances produce these effects?
- A. Formaldehyde and formic acid (Correct Answer)
- B. Acetaldehyde
- C. Pyridine
- D. Acetic acid
Explanation: **Explanation:** The toxicity of methyl alcohol (methanol) is not primarily due to the alcohol itself, but rather its metabolic byproducts [2]. Methanol is metabolized in the liver by the enzyme **alcohol dehydrogenase** into **formaldehyde**, which is then rapidly converted by **aldehyde dehydrogenase** into **formic acid** [1]. 1. **Formaldehyde:** This is a highly reactive compound that causes direct cellular damage and is primarily responsible for the retinal toxicity and subsequent **optic nerve atrophy** (leading to "snowstorm vision" or blindness) [2]. 2. **Formic Acid:** This metabolite inhibits mitochondrial cytochrome oxidase, leading to cellular hypoxia and profound **metabolic acidosis** (high anion gap). The accumulation of formate is responsible for the **CNS depression** and **cardiac depression** seen in severe poisoning. **Analysis of Incorrect Options:** * **B. Acetaldehyde:** This is the primary metabolite of **ethanol** (ethyl alcohol). While it causes the "hangover" effect and flushing, it does not cause optic atrophy [3]. * **C. Pyridine:** A basic heterocyclic organic compound used as a solvent; it is not a metabolite of methanol and has a different toxicity profile. * **D. Acetic acid:** This is the end-product of ethanol metabolism (formed from acetaldehyde). It is non-toxic and enters the Kreb’s cycle [1]. **High-Yield Clinical Pearls for NEET-PG:** * **Antidote of Choice:** **Fomepizole** (inhibits alcohol dehydrogenase) [2]. * **Alternative Antidote:** **Ethanol** (has a higher affinity for alcohol dehydrogenase, preventing methanol metabolism) [2]. * **Adjuvant Therapy:** **Folate/Leucovorin** is administered to enhance the breakdown of formic acid into CO₂ and water. * **Classic Presentation:** Metabolic acidosis with an increased anion gap and osmolar gap, plus visual disturbances.
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General Anesthetics
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Local Anesthetics
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Drugs of Abuse and Addiction
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Hallucinogens
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