Central Nervous System Pharmacology — MCQs

Central Nervous System Pharmacology Indian Medical PG Practice Questions and MCQs

Question 581: Which drug is approved for obesity treatment along with Phentermine?

A. Topiramate (Correct Answer)
B. Sibutramine
C. Fenfluramine
D. Lorcaserin

Explanation: **Explanation:** The correct answer is **Topiramate**. The FDA-approved fixed-dose combination of **Phentermine and Topiramate (extended-release)** is a potent pharmacological intervention for chronic weight management. **Mechanism of Action:** * **Phentermine:** A sympathomimetic amine that acts as an appetite suppressant by increasing norepinephrine release in the hypothalamus. * **Topiramate:** An antiepileptic drug that aids weight loss through multiple mechanisms, including GABA modulation, carbonic anhydrase inhibition, and glutamate antagonism, which collectively increase satiety and reduce cravings. **Why other options are incorrect:** * **Sibutramine:** A SNRI formerly used for obesity but **withdrawn globally** due to increased risks of non-fatal myocardial infarction and stroke (SCOUT trial). * **Fenfluramine:** An older serotonergic drug withdrawn due to risks of **cardiac valvulopathy** and pulmonary hypertension. It is currently only used in very low doses for Dravet syndrome. * **Lorcaserin:** A selective 5-HT2C receptor agonist that was **withdrawn from the market** in 2020 due to an increased risk of cancer (CAMELLIA-TIMI 61 trial). **High-Yield Clinical Pearls for NEET-PG:** * **Teratogenicity:** Topiramate is associated with **cleft lip/palate**; therefore, the combination is contraindicated in pregnancy (Category X). A negative pregnancy test is mandatory before starting therapy. * **Side Effects:** Common side effects include paresthesia, dizziness, dysgeusia (metallic taste), and insomnia. * **Other Obesity Drugs to Remember:** **Orlistat** (inhibits gastric/pancreatic lipases), **Liraglutide/Semaglutide** (GLP-1 agonists), and **Naltrexone/Bupropion** combination.

Question 582: Disulfiram and acamprosate are primarily used for which of the following conditions?

A. Alcohol abstinence (Correct Answer)
B. Cocaine abuse
C. Opium poisoning
D. Atropine overdose

Explanation: **Explanation:** The correct answer is **Alcohol abstinence**. Both Disulfiram and Acamprosate are FDA-approved pharmacological interventions used to maintain sobriety in patients with Alcohol Use Disorder (AUD). * **Disulfiram (Aversion Therapy):** It acts by irreversibly inhibiting the enzyme **Aldehyde Dehydrogenase**. This leads to the accumulation of toxic **Acetaldehyde** if alcohol is consumed, causing the "Disulfiram-like reaction" (flushing, tachycardia, nausea, and palpitations). It acts as a psychological deterrent. * **Acamprosate (Anti-craving):** It is a structural analogue of GABA. It acts as a weak NMDA receptor antagonist and a $GABA_A$ receptor activator. It helps restore the neurochemical balance (GABA/Glutamate) disrupted by chronic alcohol use, thereby reducing withdrawal symptoms and cravings. **Why other options are incorrect:** * **Cocaine abuse:** Management is primarily supportive. No specific FDA-approved drug exists, though Topiramate or Modafinil are sometimes used off-label. * **Opium poisoning:** The specific antidote is **Naloxone** (opioid antagonist). * **Atropine overdose:** The treatment of choice is **Physostigmine**, a reversible acetylcholinesterase inhibitor that crosses the blood-brain barrier. **High-Yield Clinical Pearls for NEET-PG:** * **Naltrexone:** Another first-line drug for alcohol dependence; it reduces the "reward" or euphoria of drinking by blocking mu-opioid receptors. * **Acamprosate** is preferred in patients with **liver disease** (as it is renally excreted), whereas **Naltrexone** is preferred in patients with **renal failure** (as it is hepatically metabolized). * **Disulfiram-like reaction** can also be caused by drugs like Metronidazole, Cefotetan, and Sulfonylureas.

Question 583: Which of the following statements regarding methadone is TRUE, EXCEPT?

A. It is a long-acting u-receptor agonist.
B. It is rapidly absorbed from the gastrointestinal tract and is detected in plasma 30 minutes after oral administration.
C. The primary use of methadone is relief of chronic pain.
D. The onset of analgesia is 30-60 minutes after parenteral administration and 1-2 hours after oral administration. (Correct Answer)

Explanation: **Explanation** The question asks for the **incorrect** statement regarding Methadone (an "EXCEPT" question). **1. Why Option D is the Correct Answer (The Incorrect Statement):** The onset of analgesia for Methadone is actually **faster** than stated in the option. After parenteral administration (SC/IM), the onset of action is typically **10–20 minutes**, and after oral administration, it is approximately **30–60 minutes**. The values provided in Option D (30-60 min parenteral / 1-2 hours oral) are inaccurate and represent a delayed onset compared to clinical reality. **2. Analysis of Other Options (True Statements):** * **Option A:** Methadone is a potent, synthetic **$\mu$-opioid receptor agonist**. It is characterized by its **long half-life** (typically 15–40 hours, extending up to 150 hours with chronic use), making it ideal for preventing withdrawal symptoms. * **Option B:** It has excellent oral bioavailability (approx. 80%). It is **rapidly absorbed** from the GI tract and can be detected in the plasma within 30 minutes of ingestion. * **Option C:** While famous for addiction management, the **primary clinical use** of methadone in many settings is the relief of **chronic, severe pain** (especially cancer pain) and neuropathic pain, due to its NMDA receptor antagonist properties. **3. NEET-PG High-Yield Clinical Pearls:** * **Mechanism:** $\mu$-agonist + **NMDA receptor antagonist** + SNRI (inhibits reuptake of Serotonin/NE). * **Opioid De-addiction:** Used in **Maintenance Therapy** for heroin addicts because it prevents withdrawal without producing the "high" (due to slow onset and long duration). * **ECG Warning:** Methadone can cause **QT interval prolongation** and *Torsades de Pointes*; baseline ECG is recommended. * **Metabolism:** Metabolized by **CYP3A4** and **CYP2B6** in the liver.

Question 584: What is the primary site of action for opioid receptors?

A. Area postrema (Correct Answer)
B. Dorsal horn
C. Injury site
D. Brain

Explanation: **Explanation:** The **Area Postrema**, located in the floor of the fourth ventricle, is the primary site responsible for the **emetogenic (nausea and vomiting)** effects of opioids. It contains the **Chemoreceptor Trigger Zone (CTZ)**, which is rich in opioid receptors (specifically mu and kappa). Unlike most of the brain, the area postrema lacks a blood-brain barrier, allowing it to detect circulating toxins or drugs directly, triggering the vomiting reflex. **Analysis of Options:** * **B. Dorsal Horn:** While the dorsal horn of the spinal cord is a major site for the **analgesic** action of opioids (where they inhibit the release of Substance P), it is not considered the "primary" site in the context of this specific question's focus on the CTZ/Area Postrema. * **C. Injury Site:** Opioids primarily act centrally. While some peripheral opioid receptors exist (especially in inflamed tissue), their contribution to systemic opioid effects is minimal compared to central mechanisms. * **D. Brain:** This is too broad. While opioids act on various brain regions (like the Periaqueductal Gray for analgesia), the Area Postrema is the specific anatomical landmark frequently tested in exams regarding the direct chemical stimulation of the emetic pathway. **High-Yield Clinical Pearls for NEET-PG:** * **Triple Action on Emesis:** Opioids cause vomiting via 1) Direct stimulation of the CTZ, 2) Increasing vestibular sensitivity, and 3) Delaying gastric emptying. * **Tolerance:** While tolerance develops to most opioid effects (analgesia, sedation, respiratory depression), it **never** develops to **miosis (pinpoint pupils)** and **constipation**. * **Antidote:** Naloxone is the drug of choice for acute opioid overdose (competitive antagonist).

Question 585: A newborn developed respiratory depression in a postoperative ward. Which of the following medications can cause this?

A. Opioid (Correct Answer)
B. Propofol
C. Furosemide
D. Heparin

Explanation: **Explanation:** **Correct Option: A (Opioid)** Opioids (such as Morphine or Fentanyl) are the most common pharmacological cause of postoperative respiratory depression. They act as agonists at **mu (μ) receptors** in the brainstem respiratory centers. This leads to a decreased sensitivity of the respiratory center to carbon dioxide (CO2), resulting in a reduced respiratory rate and tidal volume. Newborns are particularly vulnerable because their blood-brain barrier is immature, and their metabolic pathways for drug clearance (glucuronidation) are not fully developed, leading to prolonged drug effects. **Incorrect Options:** * **B. Propofol:** While Propofol is an intravenous anesthetic that can cause transient apnea during induction, it has a very short half-life. It is rarely the cause of sustained postoperative respiratory depression once the infusion is stopped. * **C. Furosemide:** This is a loop diuretic used to manage fluid overload. Its primary side effects are electrolyte imbalances (hypokalemia) and ototoxicity, not respiratory depression. * **D. Heparin:** This is an anticoagulant used to prevent thrombosis. Its major adverse effect is bleeding/hemorrhage; it has no direct effect on the central nervous system or respiratory drive. **Clinical Pearls for NEET-PG:** * **Antidote:** The specific antagonist for opioid-induced respiratory depression is **Naloxone** (competitive μ-receptor antagonist). * **Triad of Opioid Overdose:** Pinpoint pupils (miosis), respiratory depression, and altered mental status (coma). * **Exception:** Pethidine (Meperidine) is an opioid that typically causes **mydriasis** (due to its atropine-like action) rather than miosis. * **Safe Opioid in Renal Failure:** Fentanyl is preferred as it lacks active metabolites (unlike Morphine).

Question 586: Which antiepileptic drug is considered the safest for use during pregnancy?

A. Dilantin
B. Sodium valproate
C. Trimethadione
D. Carbamazepine (Correct Answer)

Explanation: **Explanation:** The management of epilepsy during pregnancy requires balancing maternal seizure control with the risk of teratogenicity. While no antiepileptic drug (AED) is entirely risk-free, **Carbamazepine** is considered one of the safer options among the traditional AEDs listed. **1. Why Carbamazepine is the Correct Choice:** Among the options provided, Carbamazepine has a lower incidence of major congenital malformations (approx. 2–3%) compared to Valproate. While it is associated with a specific risk of neural tube defects (NTDs), this risk is significantly lower than that of Valproate and can be partially mitigated with high-dose Folic acid supplementation. In clinical practice, Levetiracetam and Lamotrigine are now preferred, but within this specific list, Carbamazepine is the safest. **2. Why Other Options are Incorrect:** * **Sodium Valproate:** This is the **most teratogenic** AED. It is associated with "Fetal Valproate Syndrome," characterized by a high risk of neural tube defects (spina bifida), craniofacial abnormalities, and cognitive impairment. It is generally contraindicated in pregnancy unless no other drug works. * **Dilantin (Phenytoin):** Causes "Fetal Hydantoin Syndrome," which includes cleft lip/palate, microcephaly, and hypoplastic phalanges/nails. * **Trimethadione:** This drug is highly teratogenic, causing "Fetal Trimethadione Syndrome" (V-shaped eyebrows, low-set ears, and cardiac defects). It is rarely used in modern practice. **High-Yield Clinical Pearls for NEET-PG:** * **Safest overall (Modern):** Levetiracetam and Lamotrigine are currently the drugs of choice for pregnant women. * **Most Teratogenic:** Valproate (highest risk of NTDs). * **Folic Acid:** All women of childbearing age on AEDs should take 4–5 mg of Folic acid daily to reduce NTD risk. * **Vitamin K:** Enzyme-inducing AEDs (Phenytoin, Carbamazepine) can cause neonatal hemorrhage; Vitamin K is administered to the mother in the last month of pregnancy.

Question 587: Osteomalacia is an adverse effect of which of the following drugs?

A. Primidone
B. Phenytoin (Correct Answer)
C. Carbamazepine
D. Valproic acid

Explanation: **Explanation:** **Phenytoin** is a classic cause of **osteomalacia** (in adults) and rickets (in children) due to its effect on Vitamin D metabolism. **Mechanism:** Phenytoin is a potent **inducer of Cytochrome P450 (CYP) enzymes** in the liver. This induction accelerates the catabolism of Vitamin D into inactive metabolites. Consequently, there is a decrease in intestinal calcium absorption, leading to hypocalcemia. This triggers a secondary rise in Parathyroid Hormone (PTH), which mobilizes calcium from the bones, resulting in decreased bone mineral density and osteomalacia. **Analysis of Options:** * **A. Primidone:** While Primidone is an enzyme inducer and can theoretically cause bone loss, Phenytoin is the most classically associated and frequently tested drug for this specific adverse effect in competitive exams. * **C. Carbamazepine:** Like Phenytoin, it is an enzyme inducer and can cause bone loss, but Phenytoin has a more profound and well-documented clinical association with overt osteomalacia. * **D. Valproic Acid:** It is an enzyme **inhibitor**. While it can cause bone loss through different mechanisms (e.g., direct effect on osteoblasts), it is not the primary answer for classical enzyme-induction-mediated osteomalacia. **Clinical Pearls for NEET-PG:** * **Gingival Hyperplasia:** Another high-yield side effect of Phenytoin (due to increased PDGF). * **Fetal Hydantoin Syndrome:** Characterized by hypoplastic phalanges, cleft lip/palate, and microcephaly. * **Zero-order Kinetics:** Phenytoin follows saturation kinetics at therapeutic/higher doses. * **Prophylaxis:** Patients on long-term Phenytoin should be monitored for Vitamin D levels and may require Calcium and Vitamin D supplementation.

Question 588: Cleft lip is caused by which of the following drugs?

A. Levetiracetam
B. Phenytoin (Correct Answer)
C. Sodium valproate
D. Phenobarbitone

Explanation: Phenytoin is the correct answer because it is classically associated with Fetal Hydantoin Syndrome. This syndrome occurs due to the production of epoxide metabolites during phenytoin metabolism, which are teratogenic. The hallmark features include cleft lip and cleft palate, microcephaly, digital hypoplasia (hypoplastic nails/phalanges), and cardiac defects.Analysis of Options:Sodium Valproate (Option C): While highly teratogenic, it is most specifically associated with Neural Tube Defects (e.g., Spina Bifida) [1] due to its interference with folate metabolism. It can cause "Fetal Valproate Syndrome" (craniofacial dysmorphism), but cleft lip is more classically linked to Phenytoin in exams.Phenobarbitone (Option D): This drug is associated with cardiac defects and hemorrhage in the newborn (due to Vitamin K deficiency), but it is not the primary drug linked to isolated cleft lip/palate.Levetiracetam (Option A): This is considered one of the safest antiepileptic drugs during pregnancy, along with Lamotrigine. It has a much lower risk of major congenital malformations.High-Yield NEET-PG Pearls:Drug of Choice (DOC) for Epilepsy in Pregnancy: Levetiracetam or Lamotrigine.Folate Supplementation: All women on AEDs should take high-dose Folic acid (5mg) to reduce the risk of neural tube defects.Enzyme Induction: Phenytoin, Phenobarbitone, and Carbamazepine are enzyme inducers that can decrease Vitamin K levels; thus, Vitamin K prophylaxis is given to the mother in the last month of pregnancy to prevent neonatal hemorrhage.

Question 589: Which of the following statements regarding the use of antiepileptic drugs in pregnancy is true?

A. Valproate is associated with neural tube defects. (Correct Answer)
B. Multiple antiepileptic drugs should be administered.
C. Carbamazepine is used as monotherapy.
D. Phenytoin can produce fetal hydantoin syndrome.

Explanation: **Explanation:** **1. Why Option A is Correct:** Sodium Valproate is highly teratogenic and is specifically associated with **Neural Tube Defects (NTDs)**, such as spina bifida, in approximately 1-2% of exposed pregnancies. This occurs because valproate interferes with folate metabolism. It is also linked to "Fetal Valproate Syndrome," characterized by craniofacial abnormalities, cardiovascular defects, and cognitive impairment. **2. Analysis of Incorrect Options:** * **Option B:** Polytherapy significantly increases the risk of congenital malformations. The clinical goal in pregnancy is to maintain seizure control using **monotherapy** at the lowest effective dose to minimize fetal risk. * **Option C:** While Carbamazepine can be used as monotherapy, it is not the *only* drug used, nor is it the safest. It is also associated with a risk of NTDs (though lower than valproate). Currently, **Levetiracetam and Lamotrigine** are preferred first-line agents in pregnancy due to their lower teratogenic potential. * **Option D:** While this statement is medically true (Phenytoin causes Fetal Hydantoin Syndrome), in the context of standard NEET-PG questions, **Option A** is the most "classic" and frequently tested association regarding specific malformations (NTDs) and valproate. *Note: If this were a "Multiple Correct" format, D would be true, but A remains the highest-yield clinical fact.* **3. High-Yield Clinical Pearls for NEET-PG:** * **Folic Acid:** All women of childbearing age on AEDs should receive high-dose folic acid (5 mg/day) pre-conceptionally to reduce NTD risk. * **Vitamin K:** Enzyme-inducing AEDs (Phenytoin, Carbamazepine, Phenobarbital) can cause neonatal hemorrhage; Vitamin K prophylaxis is given to the mother in the last month of pregnancy and to the newborn. * **Drug of Choice:** Levetiracetam is currently favored for its superior safety profile in pregnancy.

Question 590: Which of the following statements regarding drugs used in Parkinsonism is true?

A. Amantadine is a cholinergic drug.
B. Vitamin B6 enhances the action of Levodopa.
C. COMT inhibitors prolong the action of Levodopa. (Correct Answer)
D. None of the above.

Explanation: **Explanation:** **1. Why Option C is Correct:** Levodopa is metabolized in the periphery by two main enzymes: Dopa decarboxylase (DDC) and **Catechol-O-methyltransferase (COMT)**. While DDC inhibitors (Carbidopa) are routinely used, COMT still converts Levodopa into 3-O-methyldopa, reducing its availability to the brain. **COMT inhibitors** (e.g., Entacapone, Tolcapone) block this pathway, decreasing the peripheral degradation of Levodopa. This increases its plasma half-life and ensures a more sustained delivery to the CNS, thereby **prolonging its duration of action** and helping manage "wearing-off" phenomena. **2. Why Other Options are Incorrect:** * **Option A:** Amantadine is an **antiviral** drug that acts as a **dopaminergic** agent (increasing dopamine release and inhibiting reuptake) and an NMDA antagonist. It is not a cholinergic drug; in fact, it possesses mild anticholinergic properties. * **Option B:** Vitamin B6 (Pyridoxine) is a cofactor for the enzyme Dopa decarboxylase. It **accelerates the peripheral metabolism** of Levodopa into Dopamine. Since Dopamine cannot cross the blood-brain barrier, Vitamin B6 actually **decreases** the effectiveness of Levodopa (unless a DDC inhibitor like Carbidopa is also used). **3. High-Yield Clinical Pearls for NEET-PG:** * **Entacapone** acts only peripherally, while **Tolcapone** acts both peripherally and centrally (but is associated with hepatotoxicity). * **Amantadine** is the drug of choice for Levodopa-induced dyskinesias and can cause **Livedo Reticularis** (mottled skin discoloration). * **"On-off" phenomenon** is a long-term complication of Levodopa therapy characterized by fluctuations in motor performance. * **Bromocriptine** is an Ergot-derived dopamine agonist, whereas **Pramipexole and Ropinirole** are non-ergot derivatives (preferred due to fewer side effects like pulmonary fibrosis).

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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