Central Nervous System Pharmacology — MCQs
On this page
The antiepileptic drug lacosamide acts by:
Which drug has inverse agonist activity at benzodiazepine receptors?
What is the recommended rate of intravenous injection for Valium?
Which of the following is a known side effect of ketamine?
Which of the following can be used in the treatment of myoclonic seizures, except?
Which of the following is a long-acting barbiturate?
What is the drug of choice for the prevention of seizures in a patient with severe preeclampsia?
Which anti-Parkinsonism drug is a selective COMT inhibitor?
Which CB1 antagonist is used in smoking cessation?
If carbamazepine is added to valproate, which side effect of valproate can increase?
Central Nervous System Pharmacology Indian Medical PG Practice Questions and MCQs
Question 21: The antiepileptic drug lacosamide acts by:
- A. Inhibiting synaptic vesicular protein
- B. Inhibiting CRMP protein (Correct Answer)
- C. Inhibiting GABA metabolism
- D. Inhibiting glutamate release
Explanation: **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).
Question 22: Which drug has inverse agonist activity at benzodiazepine receptors?
- A. Flumazenil
- B. Beta carboline (Correct Answer)
- C. Naltrexone
- D. Zopiclone
Explanation: **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.
Question 23: What is the recommended rate of intravenous injection for Valium?
- A. 1 ml per minute (Correct Answer)
- B. 2.5 ml per minute
- C. 1 mg per minute
- D. 2.5 mg per minute
Explanation: **Explanation:** The correct answer is **A. 1 ml per minute.** **Why it is correct:** Valium (Diazepam) is a highly lipid-soluble benzodiazepine commonly used for status epilepticus and acute anxiety. When administered intravenously, it must be injected slowly to prevent serious adverse effects. The standard recommendation is a rate not exceeding **5 mg per minute** for adults. Since the standard concentration of Diazepam injection is **5 mg/ml**, this translates to a rate of **1 ml per minute**. Slow administration is crucial because rapid bolus injection can lead to severe respiratory depression, apnea, or hypotension. **Analysis of Incorrect Options:** * **B. 2.5 ml per minute:** This rate is too fast (equivalent to 12.5 mg/min), significantly increasing the risk of cardiovascular collapse and respiratory arrest. * **C. 1 mg per minute:** While safe, this is slower than the standard clinical recommendation for acute management. * **D. 2.5 mg per minute:** Although this rate is technically safe (as it is below the 5 mg/min limit), it does not match the standard "1 ml per minute" guideline taught in pharmacological textbooks and clinical protocols for the 5 mg/ml preparation. **High-Yield Clinical Pearls for NEET-PG:** * **Vehicle:** Diazepam is insoluble in water and is dissolved in **propylene glycol**. Rapid injection of this vehicle can cause venous thrombosis and phlebitis. * **Dilution:** Diazepam should **not** be diluted with or added to other IV fluids, as it may precipitate. * **Pediatric Dosing:** In children, the rate should be even slower (not exceeding 0.25 mg/kg over 3 minutes). * **Antidote:** In case of benzodiazepine overdose or severe respiratory depression, the specific antagonist is **Flumazenil**.
Question 24: Which of the following is a known side effect of ketamine?
- A. Hallucination (Correct Answer)
- B. Hypotension
- C. Myocardial depression
- D. Decrease in intracranial pressure
Explanation: **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.
Question 25: Which of the following can be used in the treatment of myoclonic seizures, except?
- A. Valproate
- B. Carbamazepine (Correct Answer)
- C. Topiramate
- D. Zonisamide
Explanation: **Explanation:** The correct answer is **Carbamazepine**. In the management of epilepsy, it is crucial to distinguish between narrow-spectrum and broad-spectrum antiepileptic drugs (AEDs). **Myoclonic seizures** are generalized seizures that typically respond to broad-spectrum agents but can be significantly **aggravated or worsened** by certain narrow-spectrum sodium channel blockers. 1. **Why Carbamazepine is the correct answer:** Carbamazepine (along with Phenytoin and Vigabatrin) is known to exacerbate myoclonic and absence seizures. Its mechanism involves prolonging the inactivated state of sodium channels, which, while effective for focal seizures, can destabilize the thalamocortical rhythms involved in myoclonus. 2. **Why the other options are incorrect:** * **Valproate (Option A):** The drug of choice for myoclonic seizures (specifically Juvenile Myoclonic Epilepsy). It has a broad mechanism of action affecting sodium channels, T-type calcium channels, and GABA levels. * **Topiramate (Option C):** A broad-spectrum AED that is effective against multiple seizure types, including myoclonic jerks, due to its multiple mechanisms (Na+ channel block, AMPA/Kainate antagonism, and GABA enhancement). * **Zonisamide (Option D):** Another broad-spectrum agent with sulfonamide structure that is effective in treating myoclonic seizures. **NEET-PG High-Yield Pearls:** * **Drugs that worsen Myoclonus/Absence:** Carbamazepine, Phenytoin, Gabapentin, Pregabalin, and Vigabatrin. * **Drug of Choice for JME (Juvenile Myoclonic Epilepsy):** Valproate (Leveitiracetam is a preferred alternative in females of childbearing age due to valproate's teratogenicity). * **Broad Spectrum AEDs:** Valproate, Lamotrigine, Topiramate, Zonisamide, and Levetiracetam.
Question 26: Which of the following is a long-acting barbiturate?
- A. Thiopentone
- B. Secobarbitone
- C. Phenobarbitone (Correct Answer)
- D. Pentobarbitone
Explanation: **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].
Question 27: What is the drug of choice for the prevention of seizures in a patient with severe preeclampsia?
- A. Phenytoin
- B. Magnesium sulphate (Correct Answer)
- C. Diazepam
- D. Nifedipine
Explanation: **Magnesium sulphate ($MgSO_4$)** is the gold standard and drug of choice for both the **prevention (prophylaxis)** of seizures in preeclampsia and the **treatment** of seizures in eclampsia. Its superiority over traditional anticonvulsants was established by the landmark **Magpie Trial** [1]. **Magnesium sulfate** is used for seizure prevention in women with severe preeclampsia, based on its documented efficacy and lack of adverse effects on the mother or baby [1]. **Mechanism of Action:** $MgSO_4$ acts as a CNS depressant by blocking **NMDA receptors** and acting as a non-specific **Calcium channel blocker**. It decreases acetylcholine release at the neuromuscular junction and causes cerebral vasodilation, reducing cerebral ischemia. **Analysis of Incorrect Options:** * **Phenytoin (A):** While an effective antiepileptic, it is less effective than $MgSO_4$ in preventing eclamptic seizures and carries a risk of teratogenicity (Fetal Hydantoin Syndrome). * **Diazepam (C):** A benzodiazepine used for status epilepticus, but in eclampsia, it is associated with a higher risk of seizure recurrence and neonatal respiratory depression compared to $MgSO_4$. * **Nifedipine (D):** This is a calcium channel blocker used as an **antihypertensive** to manage high blood pressure in preeclampsia, but it has no intrinsic anticonvulsant properties. **High-Yield Clinical Pearls for NEET-PG:** * **Therapeutic Window:** 4–7 mEq/L. * **Monitoring:** Always check for **Patellar reflex** (first sign of toxicity is loss of reflex), **Respiratory rate** (>12/min), and **Urine output** (>30 ml/hr). * **Antidote:** 10% **Calcium Gluconate** (10 ml IV over 10 mins). * **Regimens:** Pritchard (IM) and Zuspan (IV) are the standard dosing schedules.
Question 28: Which anti-Parkinsonism drug is a selective COMT inhibitor?
- A. Entacapone (Correct Answer)
- B. Ropinirole
- C. Pergolide
- D. Pramipexole
Explanation: **Explanation:** **Entacapone** is a selective and reversible inhibitor of the enzyme **Catechol-O-methyltransferase (COMT)**. In Parkinson’s disease management, when Levodopa is administered, it is metabolized peripherally by DOPA decarboxylase and COMT. While Carbidopa inhibits decarboxylation, COMT becomes the dominant pathway, converting Levodopa into 3-O-methyldopa. Entacapone acts primarily in the **periphery** to block this conversion, thereby increasing the bioavailability of Levodopa and extending its half-life. This helps reduce "off-time" and the "wearing-off" effect in patients on long-term Levodopa therapy. **Analysis of Incorrect Options:** * **Ropinirole and Pramipexole (Options B & D):** These are **Non-ergot Dopamine Agonists**. They act directly on dopamine receptors (specifically D2 and D3) and do not inhibit metabolic enzymes. They are often used as monotherapy in early Parkinson’s or as adjuncts to Levodopa. * **Pergolide (Option C):** This is an older **Ergot-derivative Dopamine Agonist**. Its use has significantly declined due to the risk of cardiac valvular fibrosis. **High-Yield Clinical Pearls for NEET-PG:** * **Tolcapone vs. Entacapone:** Tolcapone inhibits COMT both **peripherally and centrally**, but it is rarely used due to severe **hepatotoxicity**. Entacapone is preferred as it is not hepatotoxic and acts only peripherally. * **Side Effect:** COMT inhibitors can cause a harmless **orange-discoloration of urine**. * **Triple Therapy:** The combination of Levodopa + Carbidopa + Entacapone is available as a single formulation to improve compliance.
Question 29: Which CB1 antagonist is used in smoking cessation?
- A. Naloxona
- B. Rimonabant (Correct Answer)
- C. Varenicline
- D. Bupropion
Explanation: **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.
Question 30: If carbamazepine is added to valproate, which side effect of valproate can increase?
- A. Thrombocytopenia
- B. Hepatotoxicity (Correct Answer)
- C. Hyperammonemia
- D. Pancreatitis
Explanation: **Explanation:** The correct answer is **Hepatotoxicity**. **Mechanism of Interaction:** Valproate is primarily metabolized in the liver. When **Carbamazepine** (a potent **Cytochrome P450 enzyme inducer**) is added, it accelerates the metabolism of valproate. This induction shifts the metabolic pathway toward the production of **4-pentenoic acid** (4-en-VPA) and other reactive unsaturated metabolites. These metabolites are highly hepatotoxic and are responsible for the microvesicular steatosis and liver injury associated with valproate therapy. Therefore, enzyme-inducing drugs like carbamazepine or phenytoin significantly increase the risk of valproate-induced liver damage. **Analysis of Incorrect Options:** * **A. Thrombocytopenia:** This is a dose-related side effect of valproate due to bone marrow suppression or peripheral destruction of platelets. It is not specifically potentiated by enzyme induction. * **C. Hyperammonemia:** Valproate causes hyperammonemia by interfering with the urea cycle (inhibiting carbamoyl phosphate synthetase I). While common, its risk is more closely linked to valproate dosage and carnitine deficiency rather than carbamazepine co-administration. * **D. Pancreatitis:** This is an idiosyncratic (unpredictable) reaction to valproate. It is not known to be exacerbated by the metabolic induction caused by carbamazepine. **High-Yield Clinical Pearls for NEET-PG:** * **Valproate's "Black Box" Warnings:** Hepatotoxicity (especially in children <2 years), Pancreatitis, and Teratogenicity (Neural tube defects). * **Enzyme Status:** Valproate is an **Enzyme Inhibitor**, whereas Carbamazepine is an **Enzyme Inducer** (and an auto-inducer). * **Drug of Choice:** Valproate remains the drug of choice for generalized seizures (Myoclonic, Absence, and Tonic-Clonic). * **Monitoring:** Liver Function Tests (LFTs) are mandatory during the first 6 months of valproate therapy, especially if used in polytherapy.
Practice by Chapter
General Anesthetics
Practice Questions
Local Anesthetics
Practice Questions
Sedative-Hypnotics
Practice Questions
Antiepileptic Drugs
Practice Questions
Antiparkinsonian Drugs
Practice Questions
Opioid Analgesics
Practice Questions
Drugs of Abuse and Addiction
Practice Questions
Psychostimulants
Practice Questions
Hallucinogens
Practice Questions
CNS Stimulants and Cognitive Enhancers
Practice Questions
Want unlimited practice?
Get full access to all questions, explanations, and performance tracking.
Start For Free