Central Nervous System Pharmacology Practice Questions

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.

Q: A patient with Parkinsonism is managed with levodopa. What happens if Vitamin B complex is administered concurrently to the patient?

Decreased efficacy will result.. The correct answer is **D. Decreased efficacy will result.** **Mechanism of Interaction:** Levodopa is a precursor to dopamine that must cross the blood-brain barrier (BBB) to be effective. In the periphery, levodopa is converted to dopamine by the enzyme **Dopa decarboxylase (DDC)** [1]. Vitamin B6 (Pyridoxine), a common component of Vitamin B complex, acts as a **cofactor** for DDC. When administered concurrently, Pyridoxine accelerates the peripheral decarboxylation of levodopa into dopamine. Since dopamine cannot cross the BBB, less levodopa remains available to enter the brain, leading to a significant reduction in therapeutic efficacy [1]. **Analysis of Incorrect Options:** * **Option A:** The action is not potentiated; it is diminished because the drug is "wasted" in the systemic circulation before reaching its target site. * **Option B:** Decarboxylation in the brain is not the primary issue; rather, it is the **increased peripheral decarboxylation** that prevents the drug from reaching the brain. * **Option C:** Side effects are actually **increased**. Higher peripheral dopamine levels lead to greater activation of systemic receptors, causing nausea, vomiting, and cardiac arrhythmias. **NEET-PG High-Yield Pearls:** * **The Carbidopa Solution:** Modern formulations combine Levodopa with **Carbidopa** (a peripheral DDC inhibitor). Carbidopa does not cross the BBB, so it prevents peripheral conversion but allows central conversion [1]. * **Pyridoxine Paradox:** The interaction between Vitamin B6 and Levodopa **does not occur** if the patient is taking the Levodopa-Carbidopa combination, as Carbidopa effectively blocks the Pyridoxine-enhanced peripheral metabolism. * **Dietary Advice:** Patients on plain Levodopa should be advised to avoid high-protein meals (which compete for transport) and excessive Pyridoxine intake.

Q: Hyponatremia is a known side effect of which of the following medications?

Carbamazepine. **Explanation:** **Carbamazepine** is a well-known cause of **hyponatremia** (occurring in up to 10-15% of patients). The underlying mechanism is the stimulation of **Antidiuretic Hormone (ADH)** release and the sensitization of renal tubules to ADH, leading to a condition similar to SIADH (Syndrome of Inappropriate Antidiuretic Hormone secretion). This effect is dose-dependent and more common in elderly patients or those taking concomitant diuretics. **Analysis of Incorrect Options:** * **Olanzapine (A):** An atypical antipsychotic primarily associated with metabolic side effects such as weight gain, dyslipidemia, and hyperglycemia. It does not typically cause electrolyte imbalances. * **Lithium (B):** Unlike Carbamazepine, Lithium is associated with **Hypernatremia**. It causes Nephrogenic Diabetes Insipidus (NDI) by antagonizing the effects of ADH on the collecting ducts, leading to polyuria and dilute urine. * **Clonazepam (D):** A benzodiazepine that acts on GABA-A receptors. Its primary side effects are sedation, ataxia, and cognitive impairment; it has no significant effect on sodium regulation. **High-Yield Clinical Pearls for NEET-PG:** * **Oxcarbazepine**, a derivative of carbamazepine, carries an even **higher risk** of hyponatremia. * **SSRIs** (e.g., Fluoxetine, Sertraline) are the most common class of psychotropic drugs associated with SIADH/hyponatremia in the elderly. * **Monitoring:** When prescribing Carbamazepine, baseline and periodic serum sodium levels should be checked, especially if the patient develops symptoms like confusion, lethargy, or seizures. * **HLA-B*1502:** Always screen for this allele in Asian populations before starting Carbamazepine to prevent Stevens-Johnson Syndrome (SJS).

Q: Which of the following is not a new drug for Migraine?

Romosozumab. **Explanation:** The correct answer is **Romosozumab** because it is not used for migraine; it is a monoclonal antibody used to treat **severe osteoporosis** in postmenopausal women at high risk of fracture. It works by inhibiting **sclerostin**, thereby increasing bone formation and decreasing bone resorption. **Analysis of Incorrect Options:** * **Lasmiditan:** This is a first-in-class **5-HT1F receptor agonist**. Unlike triptans (5-HT1B/1D), it lacks vasoconstrictive properties, making it a safe alternative for migraine patients with cardiovascular contraindications. * **Ubrogepant & Rimegepant:** These belong to the **"Gepants"** class. they are small-molecule **CGRP (Calcitonin Gene-Related Peptide) receptor antagonists** approved for the acute treatment of migraine. Rimegepant is unique as it is approved for both acute treatment and prevention. **High-Yield Clinical Pearls for NEET-PG:** 1. **CGRP Pathway:** This is the most important recent target in migraine pharmacology. * *Monoclonal Antibodies (mAbs) for Prophylaxis:* Erenumab (targets CGRP receptor); Fremanezumab, Galcanezumab, and Eptinezumab (target CGRP ligand). * *Small Molecules (Gepants) for Acute/Prophylaxis:* Ubrogepant, Rimegepant, Atogepant. 2. **Lasmiditan Side Effect:** The most common side effect is **dizziness/somnolence**; patients are advised not to drive for 8 hours after intake. 3. **Romosozumab Warning:** It carries a boxed warning for increased risk of myocardial infarction, stroke, and cardiovascular death.

Question 1

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

Accepted Answer

Tizanidine

Answer

Chlorzoxazone

Answer

Baclofen

Answer

Pirenzepine

Question 2

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

Accepted Answer

Hyponatremia

Answer

Hypernatremia

Answer

Hyperkalemia

Answer

Hypokalemia

Question 3

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 4

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 5

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 6

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 7

Perampanel is:

Accepted Answer

AMPA antagonist

Answer

NMDA antagonist

Answer

GABA mimetic

Answer

Calcium channel inhibitor

Question 8

A patient with Parkinsonism is managed with levodopa. What happens if Vitamin B complex is administered concurrently to the patient?

Accepted Answer

Decreased efficacy will result.

Answer

The action of levodopa in the brain will be potentiated.

Answer

Decarboxylation of levodopa in the brain will be decreased.

Answer

Side effects will be ameliorated.

Question 9

Hyponatremia is a known side effect of which of the following medications?

Accepted Answer

Carbamazepine

Answer

Olanzapine

Answer

Lithium

Answer

Clonazepam

Question 10

Which of the following is not a new drug for Migraine?

Accepted Answer

Romosozumab

Answer

Lasmiditan

Answer

Ubrogepant

Answer

Rimegepant

Central Nervous System Pharmacology — MCQs

Central Nervous System Pharmacology — MCQs

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