Central Nervous System Pharmacology Practice Questions

Q: Valproic acid causes all EXCEPT-

It is an enzyme inducer. **Explanation:** The correct answer is **A (It is an enzyme inducer)** because Valproic acid is actually a potent **microsomal enzyme inhibitor**. Unlike most older antiepileptics (like Phenytoin, Carbamazepine, and Phenobarbitone) which induce CYP450 enzymes, Valproic acid inhibits them. This leads to significant drug interactions, such as increasing the plasma levels of Phenobarbital and Lamotrigine when co-administered. **Analysis of other options:** * **B (Obesity):** Weight gain is a very common side effect of Valproate therapy, often leading to metabolic issues and decreased compliance. * **C (Hirsutism):** This is a tricky point in pharmacology. While Valproate is classically associated with **alopecia** (hair loss/thinning), it is also a key cause of **Polycystic Ovarian Syndrome (PCOS)** in female patients. PCOS presents with hormonal imbalances that lead to **hirsutism** and acne. * **D (Neural tube defects):** Valproate is highly teratogenic. It interferes with folate metabolism, specifically increasing the risk of **Spina Bifida** (neural tube defects) if taken during pregnancy. **High-Yield Clinical Pearls for NEET-PG:** * **Mnemonic for Valproate Side Effects (VALPROATE):** **V**omiting, **A**lopecia, **L**iver toxicity (Hepatotoxicity), **P**ancreatitis/PCOS, **R**etention of fat (Obesity), **O**edema, **A**norexia, **T**eratogenicity, **E**nzyme inhibitor. * **Drug of Choice:** Valproate is the drug of choice for **Myoclonic seizures** and is a broad-spectrum agent used for Generalized Tonic-Clonic Seizures (GTCS) and Absence seizures. * **Hepatotoxicity:** It is contraindicated in children under 2 years due to the risk of fatal fulminant hepatitis.

Q: What is the primary classification of Baclofen?

Centrally acting muscle relaxant. **Explanation:** **Baclofen** is a structural analog of the inhibitory neurotransmitter Gamma-Aminobutyric Acid (GABA). It is classified as a **centrally acting muscle relaxant** because its primary site of action is within the spinal cord. **Mechanism of Action:** Baclofen acts as a selective **GABA-B receptor agonist**. By stimulating these receptors in the dorsal horn of the spinal cord, it induces hyperpolarization. This leads to: 1. **Presynaptic inhibition:** Reducing the release of excitatory neurotransmitters (like glutamate and aspartate). 2. **Postsynaptic inhibition:** Reducing the excitability of alpha motor neurons. The result is a reduction in the frequency and severity of muscle spasms. **Analysis of Options:** * **Option A (Correct):** It acts on the CNS (spinal cord) to reduce spasticity. * **Option B (Incorrect):** Peripherally acting relaxants (e.g., Succinylcholine, Vecuronium) act at the Neuromuscular Junction (NMJ), not the spinal cord. * **Option C (Incorrect):** Baclofen does not have a direct clinical effect on the motor endplate or muscle fibers. * **Option D (Incorrect):** **Dantrolene** is the classic "direct-acting" muscle relaxant, as it acts on the Ryanodine receptors (RyR1) of the sarcoplasmic reticulum within the muscle cell. **High-Yield Clinical Pearls for NEET-PG:** * **Drug of Choice:** Baclofen is the preferred agent for treating spasticity associated with **Multiple Sclerosis** and spinal cord injuries. * **Route:** Can be administered orally or via an **intrathecal pump** for severe cases. * **Side Effects:** Drowsiness, fatigue, and muscle weakness. * **Withdrawal Warning:** Abrupt discontinuation can lead to visual hallucinations, seizures, and rebound spasticity; it must be tapered gradually.

Q: Which of the following is NOT metabolized by cholinesterase?

Bupivacaine. ### Explanation The classification of local anesthetics (LAs) is a high-yield topic for NEET-PG. LAs are divided into two main groups based on their chemical linkage: **Esters** and **Amides**. **1. Why Bupivacaine is the Correct Answer:** Bupivacaine is an **Amide** local anesthetic. Amide LAs are primarily metabolized in the **liver** by microsomal enzymes (Cytochrome P450). They are not substrates for plasma cholinesterase. A simple mnemonic to identify amides is that their names contain two "i"s (e.g., Bup**i**vaca**i**ne, L**i**doca**i**ne, Pr**i**loca**i**ne, Rop**i**vaca**i**ne). **2. Analysis of Incorrect Options:** * **Tetracaine & Procaine (Options A & B):** These are **Ester** local anesthetics (containing only one "i" in their name). Esters are rapidly hydrolyzed by **pseudocholinesterase** (plasma cholinesterase). This results in a shorter half-life compared to amides. * **Acetylcholine (Option C):** This is a neurotransmitter that is rapidly degraded by both acetylcholinesterase (at the neuromuscular junction) and **butyrylcholinesterase** (plasma cholinesterase). **3. Clinical Pearls for NEET-PG:** * **Metabolism & Toxicity:** Patients with atypical pseudocholinesterase deficiency are at risk of prolonged effects/toxicity from ester LAs and Succinylcholine. * **Allergy:** Ester LAs are more likely to cause allergic reactions due to their metabolite, **Para-aminobenzoic acid (PABA)**. Amides rarely cause true allergies. * **Bupivacaine Specifics:** It is highly cardiotoxic (blocks sodium channels in the heart during diastole). **Intralipid (20%)** is the specific treatment for Local Anesthetic Systemic Toxicity (LAST). * **Cocaine:** The only ester LA that causes vasoconstriction (others are vasodilators).

Q: Which centrally acting muscle relaxant also possesses alpha-2 adrenergic agonist activity?

Tizanidine. **Explanation:** **Tizanidine** is the correct answer because it is a centrally acting muscle relaxant that specifically acts as a **selective alpha-2 ($\alpha_2$) adrenergic agonist**. It is structurally related to clonidine but possesses significantly less (about 1/10th to 1/50th) antihypertensive potency. Its primary mechanism involves stimulating presynaptic $\alpha_2$ receptors in the spinal cord, which inhibits the release of excitatory amino acids (like glutamate and aspartate) from spinal interneurons. This action reduces polysynaptic reflex activity, thereby decreasing muscle spasticity. **Analysis of Incorrect Options:** * **Chlorzoxazone (A):** A centrally acting muscle relaxant that works primarily at the level of the spinal cord and subcortical areas of the brain to inhibit multisynaptic reflex arcs. It does not have $\alpha_2$ agonist activity. * **Baclofen (B):** A structural analog of GABA that acts as a selective **GABA-B receptor agonist**. It induces muscle relaxation by increasing potassium conductance, leading to hyperpolarization of motor neurons. * **Pirenzepine (D):** An **M1-selective anticholinergic** drug formerly used to reduce gastric acid secretion in peptic ulcer disease. It is not a muscle relaxant. **NEET-PG High-Yield Pearls:** * **Tizanidine Side Effects:** Drowsiness, xerostomia (dry mouth), and hypotension (due to its $\alpha_2$ activity). * **Drug of Choice for Spasticity:** Baclofen is often the first-line treatment for spasticity associated with multiple sclerosis or spinal cord injury. * **Dantrolene:** Unlike the options above, this is a **peripherally acting** muscle relaxant that inhibits calcium release from the sarcoplasmic reticulum by binding to **Ryanodine receptors (RyR1)**. It is the drug of choice for Malignant Hyperthermia.

Q: What electrolyte imbalance is commonly caused by carbamazepine in the elderly?

Hyponatremia. **Explanation:** **1. Why Hyponatremia is Correct:** Carbamazepine is a well-known cause of **SIADH-like syndrome** (Syndrome of Inappropriate Antidiuretic Hormone). It acts by increasing the sensitivity of the renal tubules to ADH and potentially stimulating the central release of ADH. This leads to free water retention and dilutional hyponatremia. This side effect is particularly prevalent in the elderly (up to 10–15% of patients) due to age-related changes in water homeostasis and the frequent co-administration of other drugs like diuretics. **2. Why Other Options are Incorrect:** * **Hypernatremia (A):** Carbamazepine causes water retention, not water loss or sodium excess. Hypernatremia is more commonly associated with Lithium (via Nephrogenic Diabetes Insipidus). * **Hyperkalemia (C) & Hypokalemia (D):** Carbamazepine does not have a primary or direct effect on potassium excretion or shift. While profound hyponatremia can sometimes be seen alongside other electrolyte shifts in complex clinical scenarios, potassium imbalance is not a characteristic side effect of this drug. **3. High-Yield Clinical Pearls for NEET-PG:** * **Oxcarbazepine:** A prodrug of carbamazepine, it is actually **more likely** to cause hyponatremia than carbamazepine itself. * **Monitoring:** Always check serum sodium levels if an elderly patient on carbamazepine presents with new-onset confusion, lethargy, or seizures (which may be due to hyponatremia rather than epilepsy). * **Other Key Side Effects:** Stevens-Johnson Syndrome (associated with **HLA-B*1502** allele), Aplastic anemia, and Enzyme Induction (CYP3A4). * **Drug of Choice:** Carbamazepine remains the DOC for **Trigeminal Neuralgia**.

Q: Use of valproate during pregnancy may result in which of the following adverse outcomes?

Neural tube defect. **Explanation:** **Sodium Valproate** is a broad-spectrum antiepileptic drug, but it is highly teratogenic. The correct answer is **Neural Tube Defects (NTDs)**, specifically **spina bifida**. 1. **Mechanism of Teratogenicity:** Valproate causes NTDs in approximately 1–2% of exposed pregnancies. The primary mechanism is the inhibition of **histone deacetylase (HDAC)** and interference with **folate metabolism**, which are critical for the proper closure of the neural tube during the first trimester. 2. **Why other options are incorrect:** * **Mental Retardation:** While valproate exposure is linked to lower IQ and autism spectrum disorders (Fetal Valproate Syndrome), "Neural Tube Defect" is the classic, pathognomonic structural malformation tested in exams. * **Respiratory Depression:** This is an acute neonatal complication of maternal opioid or benzodiazepine use, not a structural teratogenic effect of valproate. * **Hydantoin Syndrome:** This is specifically associated with **Phenytoin** use during pregnancy, characterized by craniofacial dysmorphism, hypoplastic phalanges, and growth retardation. **High-Yield Clinical Pearls for NEET-PG:** * **Fetal Valproate Syndrome:** Includes NTDs, atrial septal defects, cleft lip/palate, and "cupid’s bow" upper lip. * **Prevention:** High-dose folic acid (4–5 mg/day) is recommended pre-conceptionally for women on antiepileptics, though it may not fully neutralize valproate's risk. * **Drug of Choice in Pregnancy:** **Lamotrigine** and **Levetiracetam** are generally considered the safest options. * **Avoidance:** Valproate should be avoided in females of childbearing age unless no other drug is effective for their seizure type (e.g., Myoclonic seizures).

Q: Pitolisant is approved for the treatment of which of the following conditions?

Excessive daytime sleepiness in patients with narcolepsy. **Explanation:** **Pitolisant** is a first-in-class selective **Histamine H3-receptor antagonist/inverse agonist**. By blocking H3 autoreceptors in the brain, it increases the synthesis and release of histamine, a key neurotransmitter that promotes wakefulness. It is FDA-approved for the treatment of **excessive daytime sleepiness (EDS)** and **cataplexy** in adult patients with **narcolepsy**. Unlike other wake-promoting agents (e.g., Modafinil), Pitolisant is not a scheduled controlled substance, as it lacks significant abuse potential. **Analysis of Incorrect Options:** * **Option A (Tenosynovial giant cell tumor):** This is treated with **Pexidartinib**, a CSF1 receptor inhibitor. * **Option C (Polyneuropathy due to transthyretin amyloidosis):** This is treated with agents like **Patisiran** (RNA interference) or **Tafamidis** (TTR stabilizer). * **Option D (Primary myelofibrosis):** This is typically managed with JAK inhibitors like **Ruxolitinib** or **Fedratinib**. **High-Yield Clinical Pearls for NEET-PG:** * **Mechanism:** H3-receptor inverse agonist (increases histamine levels in the CNS). * **Unique Feature:** It is the first non-scheduled drug for narcolepsy (low potential for addiction). * **Contraindications:** Severe hepatic impairment. It can also prolong the **QT interval**, so caution is required with other pro-arrhythmic drugs. * **Drug Interactions:** It is a CYP2D6 substrate and a weak inducer of CYP3A4, which may reduce the efficacy of hormonal contraceptives.

Q: The action of adrenaline is potentiated in the presence of all the following anesthetics except:

Ether. **Explanation:** The core concept behind this question is **Myocardial Sensitization to Catecholamines**. Certain volatile anesthetics sensitize the myocardium to the arrhythmogenic effects of adrenaline (epinephrine), increasing the risk of ventricular arrhythmias. **1. Why Ether is the Correct Answer:** Ether is a **non-sensitizing** anesthetic. Unlike halogenated agents, ether does not sensitize the heart to adrenaline. In fact, ether causes a reflex increase in sympathetic activity, which actually supports blood pressure and heart rate without making the myocardium hyper-reactive to exogenous adrenaline. Therefore, the action of adrenaline is not potentiated (in terms of arrhythmia risk) by ether. **2. Analysis of Incorrect Options:** * **Halothane:** This is the "classic" sensitizer. It is highly potent in sensitizing the heart to catecholamines. Using adrenaline with halothane is strictly limited to avoid fatal ventricular fibrillation. * **Ethyl chloride:** This is an older, halogenated hydrocarbon that, like halothane, significantly sensitizes the myocardium to adrenaline. * **Cyclopropane:** Although not a halogenated gas, cyclopropane is notorious for its high potential to sensitize the heart to adrenaline, often leading to serious arrhythmias. **3. NEET-PG High-Yield Pearls:** * **Order of Sensitization:** Halothane > Cyclopropane > Trichloroethylene > Ethyl chloride. * **Modern Agents:** Isoflurane, Desflurane, and Sevoflurane have much lower sensitization potential compared to Halothane, making them safer for use when adrenaline is needed (e.g., for local hemostasis). * **Clinical Rule:** If adrenaline must be used with Halothane, the dose should not exceed **1 µg/kg**. * **Thiopentone:** It is also considered non-sensitizing to the myocardium.

Q: Perampanel is:

AMPA antagonist. **Explanation:** **Perampanel** is a first-in-class antiepileptic drug (AED) that acts as a **selective, non-competitive antagonist at the AMPA (α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid) receptor**. 1. **Why Option B is Correct:** Glutamate is the primary excitatory neurotransmitter in the brain. It acts on ionotropic receptors: NMDA, AMPA, and Kainate. AMPA receptors mediate the fast component of excitatory postsynaptic currents. By selectively blocking these receptors on postsynaptic neurons, Perampanel reduces neuronal over-excitation and prevents the spread of seizure activity. 2. **Why Other Options are Incorrect:** * **NMDA Antagonists (Option A):** Drugs like Ketamine, Memantine, and Felbamate act here. While Felbamate has NMDA antagonist properties, Perampanel is specific to AMPA. * **GABA Mimetics (Option C):** These enhance inhibitory neurotransmission. Examples include Benzodiazepines, Barbiturates, and Tiagabine. * **Calcium Channel Inhibitors (Option D):** Ethosuximide (T-type) and Gabapentin/Pregabalin (α2δ subunit of voltage-gated Ca²⁺ channels) work via this mechanism. **High-Yield Clinical Pearls for NEET-PG:** * **Indication:** Used for focal-onset seizures and primary generalized tonic-clonic seizures. * **Pharmacokinetics:** It has a very **long half-life** (~105 hours), allowing for once-daily dosing. * **Black Box Warning:** It is notorious for causing **serious neuropsychiatric events**, including aggression, hostility, irritability, and suicidal ideation. * **Metabolism:** It is metabolized by CYP3A4; therefore, enzyme-inducing AEDs (like Carbamazepine or Phenytoin) can significantly decrease its plasma concentration.

Question 1

Valproic acid causes all EXCEPT-

Accepted Answer

It is an enzyme inducer

Answer

It causes obesity

Answer

It causes hirsutism

Answer

It causes neural tube defects

Question 2

What is the primary classification of Baclofen?

Accepted Answer

Centrally acting muscle relaxant

Answer

Peripherally acting muscle relaxant

Answer

Both centrally and peripherally acting muscle relaxant

Answer

Direct acting muscle relaxant

Question 3

Which of the following is NOT metabolized by cholinesterase?

Accepted Answer

Bupivacaine

Answer

Tetracaine

Answer

Procaine

Answer

Acetylcholine

Question 4

Which centrally acting muscle relaxant also possesses alpha-2 adrenergic agonist activity?

Accepted Answer

Tizanidine

Answer

Chlorzoxazone

Answer

Baclofen

Answer

Pirenzepine

Question 5

What electrolyte imbalance is commonly caused by carbamazepine in the elderly?

Accepted Answer

Hyponatremia

Answer

Hypernatremia

Answer

Hyperkalemia

Answer

Hypokalemia

Question 6

Use of valproate during pregnancy may result in which of the following adverse outcomes?

Accepted Answer

Neural tube defect

Answer

Mental retardation

Answer

Respiratory depression

Answer

Hydantoin syndrome

Question 7

Which one of the following is an established clinical use of morphine?

Accepted Answer

Pulmonary congestion

Answer

Management of generalized anxiety disorders

Answer

Relief of pain associated with biliary colic

Answer

Treatment of cough associated with use of ACE inhibitors

Question 8

Pitolisant is approved for the treatment of which of the following conditions?

Accepted Answer

Excessive daytime sleepiness in patients with narcolepsy

Answer

Tenosynovial giant cell tumor

Answer

Polyneuropathy due to transthyretin amyloidosis

Answer

Primary myelofibrosis

Question 9

The action of adrenaline is potentiated in the presence of all the following anesthetics except:

Accepted Answer

Ether

Answer

Halothane

Answer

Ethyl chloride

Answer

Cyclopropane

Question 10

Perampanel is:

Accepted Answer

AMPA antagonist

Answer

NMDA antagonist

Answer

GABA mimetic

Answer

Calcium channel inhibitor

Central Nervous System Pharmacology — MCQs

Central Nervous System Pharmacology — MCQs

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