Central Nervous System Pharmacology — MCQs

Central Nervous System Pharmacology Indian Medical PG Practice Questions and MCQs

Question 471: Which one of the following drugs is used in Alzheimer's disease?

A. Tacrine (Correct Answer)
B. Pemoline
C. Doxapram
D. Methylphenidate

Explanation: **Explanation:** **Correct Option: A (Tacrine)** Alzheimer’s disease is characterized by a cholinergic deficiency in the brain. **Tacrine** is a centrally acting, reversible **acetylcholinesterase inhibitor (AChEI)**. By inhibiting the enzyme that breaks down acetylcholine, it increases the concentration of this neurotransmitter in the synaptic cleft, thereby improving cognitive function and memory in patients with mild-to-moderate Alzheimer's. While it was the first AChEI approved for this condition, its clinical use is now limited due to significant **hepatotoxicity** (frequent monitoring of ALT is required). **Incorrect Options:** * **B. Pemoline:** This is a CNS stimulant previously used for ADHD and narcolepsy. It is not used in Alzheimer's and has been largely withdrawn due to liver toxicity. * **C. Doxapram:** This is a **central respiratory stimulant** (analeptic). It acts on peripheral chemoreceptors to increase tidal volume and respiratory rate; it is typically used in acute respiratory failure or post-anesthesia respiratory depression. * **D. Methylphenidate:** A potent CNS stimulant (amphetamine-like) used primarily in the treatment of **ADHD** and **Narcolepsy**. It works by increasing dopamine and norepinephrine levels. **NEET-PG High-Yield Pearls:** * **First-line AChEIs for Alzheimer's:** Donepezil, Rivastigmine, and Galantamine (preferred over Tacrine due to better safety profiles). * **NMDA Receptor Antagonist:** **Memantine** is used for moderate-to-severe Alzheimer's, often as an adjunct to AChEIs. * **Rivastigmine** is unique as it is available as a **transdermal patch**, which improves compliance and reduces GI side effects. * **Galantamine** also acts as a nicotinic receptor modulator.

Question 472: Which drug can be used in the management of Sydenham’s chorea?

A. Haloperidol (Correct Answer)
B. Valproate sodium
C. Carbamazepine
D. Phenytoin

Explanation: **Explanation:** **Sydenham’s chorea** is a major manifestation of Acute Rheumatic Fever, characterized by involuntary, purposeless movements caused by autoimmune-mediated inflammation of the basal ganglia. The pathophysiology involves **dopaminergic overactivity** in the nigrostriatal pathway. **Why Haloperidol is correct:** Haloperidol is a potent **D2 receptor antagonist** (typical antipsychotic). By blocking dopamine receptors in the striatum, it effectively suppresses choreiform movements. It is considered one of the first-line pharmacological treatments for severe Sydenham’s chorea when symptoms interfere with daily activities or safety. **Analysis of Incorrect Options:** * **Valproate sodium & Carbamazepine:** While Valproate is sometimes used as a second-line alternative (due to its GABAergic effects) if dopamine antagonists are contraindicated, **Haloperidol** remains the classic, more frequently tested answer for chorea management. Carbamazepine is primarily an antiepileptic and has no established role in treating chorea. * **Phenytoin:** This is an antiepileptic drug that can actually **induce or worsen** chorea as a side effect; therefore, it is contraindicated in this clinical scenario. **Clinical Pearls for NEET-PG:** * **First-line management:** Most cases of Sydenham’s chorea are self-limiting and require only bed rest and penicillin prophylaxis. * **Drug of choice for movement control:** Haloperidol or Pimozide (D2 blockers). * **Alternative:** Sodium Valproate is preferred by some clinicians to avoid the risk of Extrapyramidal Side Effects (EPS) associated with Haloperidol. * **Steroids:** May be used in refractory cases to hasten recovery due to the autoimmune nature of the disease.

Question 473: Which of the following is NOT a mechanism of action of Levetiracetam?

A. Used in myoclonic epilepsy
B. Acts on GABA receptors
C. Inhibits postsynaptic calcium channels (Correct Answer)
D. Binds to SV2A and regulates neurotransmitter exocytosis

Explanation: Explanation: Levetiracetam is a unique broad-spectrum antiepileptic drug (AED) with a mechanism of action distinct from traditional sodium or calcium channel blockers. Why Option C is correct: Levetiracetam does not inhibit postsynaptic calcium channels. Its primary action is presynaptic. While it may inhibit N-type calcium channels and reduce intracellular calcium release from the sarcoplasmic reticulum, its hallmark mechanism is binding to the Synaptic Vesicle Protein 2A (SV2A). This binding modulates the release of neurotransmitters (like glutamate and GABA) by regulating vesicle exocytosis. Analysis of other options: * Option A (Used in myoclonic epilepsy): This is a correct clinical use. Levetiracetam is a first-line agent for myoclonic seizures (including Juvenile Myoclonic Epilepsy) and is also used for focal and generalized tonic-clonic seizures. * Option B (Acts on GABA receptors): While not its primary mechanism, Levetiracetam has been shown to reverse the inhibition of GABA and glycine-gated currents by negative modulators (like zinc and ̢-carbolines), indirectly facilitating GABAergic transmission. * Option D (Binds to SV2A): This is the most characteristic mechanism of Levetiracetam. SV2A binding correlates directly with its anticonvulsant potency. High-Yield NEET-PG Pearls: * Pharmacokinetics: It has near 100% bioavailability, minimal protein binding, and is excreted unchanged in urine (requires dose adjustment in renal failure). * Drug Interactions: It has no significant CYP450 interactions, making it ideal for patients on multiple medications. * Side Effects: The most specific side effect is behavioral changes (irritability, aggression, or "Levy-rage") and somnolence. * Brivaracetam: A newer analog with higher affinity for SV2A.

Question 474: The clinical indications for tricyclic antidepressants include all of the following except?

A. Enuresis in elderly subjects
B. Neuropathic pain
C. Panic disorder
D. Uncontrolled seizures (Correct Answer)

Explanation: **Explanation:** The correct answer is **D. Uncontrolled seizures**. **1. Why Uncontrolled Seizures is the correct answer:** Tricyclic Antidepressants (TCAs), such as Amitriptyline and Imipramine, are known to **lower the seizure threshold**. This means they make the brain more susceptible to firing abnormal electrical discharges. Consequently, TCAs are generally **contraindicated** in patients with epilepsy or a history of seizures, as they can precipitate or worsen seizure activity. In cases of TCA overdose, seizures are a common and life-threatening complication. **2. Analysis of Incorrect Options:** * **A. Enuresis in elderly subjects:** While more commonly used for nocturnal enuresis in children (due to their anticholinergic effect which increases bladder capacity), TCAs like Imipramine have historically been used for urinary incontinence in the elderly. * **B. Neuropathic Pain:** TCAs are a first-line treatment for neuropathic pain (e.g., diabetic neuropathy, post-herpetic neuralgia). They work by enhancing descending inhibitory pathways through the inhibition of norepinephrine and serotonin reuptake. * **C. Panic Disorder:** TCAs (specifically Imipramine and Clomipramine) are effective in treating panic disorder and other anxiety disorders, although SSRIs are now preferred due to a better side-effect profile. **Clinical Pearls for NEET-PG:** * **The "3 Cs" of TCA Toxicity:** Coma, Convulsions, and Cardiotoxicity (arrhythmias due to sodium channel blockade). * **Antidote for Cardiotoxicity:** Sodium bicarbonate (NaHCO₃) is used to manage QRS widening and arrhythmias in TCA overdose. * **Drug of Choice for OCD:** Clomipramine (a TCA), though SSRIs are first-line. * **Nocturnal Enuresis:** Imipramine is the TCA used, but **Desmopressin** is currently the drug of choice.

Question 475: Regarding lamotrigine, which of the following statements is true?

A. It is a dopaminergic agonist used in Parkinsonism.
B. It acts by blocking NMDA type of glutamate receptors.
C. It is a broad spectrum antiepileptic drug. (Correct Answer)
D. It suppresses tonic-clonic seizures but worsens absence seizures.

Explanation: **Explanation:** **Lamotrigine** is a versatile antiepileptic drug (AED) primarily known for its **broad-spectrum activity**. 1. **Why Option C is Correct:** Lamotrigine is effective against a wide variety of seizure types, including focal (partial) seizures and generalized seizures (tonic-clonic, absence, and myoclonic). Its primary mechanism involves **blocking voltage-gated sodium (Na+) channels** in their inactivated state, which inhibits the release of excitatory neurotransmitters like **glutamate**. 2. **Why Other Options are Incorrect:** * **Option A:** Lamotrigine has no significant dopaminergic activity and is not used to treat Parkinsonism. * **Option B:** While it reduces glutamate release, its primary molecular target is the **sodium channel**, not the NMDA receptor (unlike drugs like Memantine or Ketamine). * **Option C vs D:** Unlike older narrow-spectrum drugs (e.g., Phenytoin or Carbamazepine), which can exacerbate absence seizures, Lamotrigine is effective in treating **absence seizures**. **High-Yield Clinical Pearls for NEET-PG:** * **Stevens-Johnson Syndrome (SJS):** The most dreaded side effect of Lamotrigine is a severe skin rash (SJS/TEN). To minimize this risk, the drug must be started at a low dose and **titrated very slowly**. * **Bipolar Disorder:** Beyond epilepsy, it is a first-line agent for the **maintenance treatment of Bipolar Depression**. * **Pregnancy:** It is considered one of the **safer AEDs during pregnancy** (lower teratogenic risk compared to Valproate), though clearance increases significantly during gestation. * **Drug Interaction:** Valproate inhibits Lamotrigine metabolism, doubling its half-life and significantly increasing the risk of life-threatening rashes.

Question 476: What is the drug of choice for idiopathic intracranial hypertension?

A. Acetazolamide (Correct Answer)
B. Glycerol
C. Mannitol
D. Dexamethasone

Explanation: **Explanation:** **Idiopathic Intracranial Hypertension (IIH)**, also known as Pseudotumor Cerebri, is characterized by increased intracranial pressure (ICP) without an identifiable cause (like a tumor or obstruction). **Why Acetazolamide is the Drug of Choice:** Acetazolamide is a **Carbonic Anhydrase Inhibitor**. In the CNS, carbonic anhydrase is essential for the production of Cerebrospinal Fluid (CSF) by the choroid plexus. By inhibiting this enzyme, Acetazolamide significantly reduces the rate of CSF secretion, thereby lowering intracranial pressure. It is the first-line medical therapy, often combined with weight loss [1]. **Analysis of Incorrect Options:** * **B. Glycerol & C. Mannitol:** These are **osmotic diuretics**. While they are highly effective for the *acute* management of cerebral edema or life-threatening elevations in ICP (e.g., head injury), they are not suitable for the long-term management of IIH due to the risk of rebound ICP and electrolyte imbalances. * **D. Dexamethasone:** While glucocorticoids reduce ICP in cases of vasogenic edema (associated with brain tumors or abscesses), they are **not recommended** for IIH. In fact, steroid withdrawal can sometimes trigger or worsen IIH. **Clinical Pearls for NEET-PG:** * **Classic Presentation:** Obese female of childbearing age presenting with headache, papilledema, and "whooshing" tinnitus (pulsatile). * **Side Effects of Acetazolamide:** Paresthesia (most common), metabolic acidosis, and hypokalemia [1]. * **Alternative:** If Acetazolamide is not tolerated, **Topiramate** is an alternative as it also has weak carbonic anhydrase inhibitory activity and aids in weight loss. * **Surgical Management:** If medical therapy fails and vision is threatened, Optic Nerve Sheath Fenestration or CSF shunting is performed.

Question 477: Which of the following is NOT a first-line choice drug for epilepsy in pregnancy?

A. Carbamazepine
B. Lamotrigine
C. Levetiracetam
D. Sodium valproate (Correct Answer)

Explanation: ### Explanation **Sodium Valproate** is the correct answer because it is strictly contraindicated as a first-line agent in pregnancy due to its high **teratogenic potential**. It is associated with a significantly higher risk of major congenital malformations (MCMs) compared to other anti-epileptic drugs (AEDs). #### Why Sodium Valproate is avoided: * **Neural Tube Defects (NTDs):** It carries a 1–2% risk of spina bifida (due to interference with folate metabolism). * **Fetal Valproate Syndrome:** Characterized by craniofacial anomalies, cardiovascular defects, and limb abnormalities. * **Neurodevelopmental Delay:** Prenatal exposure is linked to lower IQ scores and increased risk of autism spectrum disorders in children. #### Why other options are incorrect: * **Lamotrigine (B) and Levetiracetam (C):** These are currently considered the **safest and preferred first-line choices** in pregnancy. They have the lowest reported rates of major malformations. * **Carbamazepine (A):** While it carries a slightly higher risk than Lamotrigine (specifically for cleft lip/palate), it is still significantly safer than Valproate and is considered a viable first-line option if the patient is already well-controlled on it. #### High-Yield Clinical Pearls for NEET-PG: 1. **Drug of Choice (DOC):** If a woman on Valproate plans pregnancy, she should be switched to **Levetiracetam** or **Lamotrigine** before conception. 2. **Folic Acid:** All pregnant women on AEDs should take high-dose folic acid (5 mg/day) to reduce NTD risks. 3. **Enzyme Inducers:** Carbamazepine and Phenytoin induce hepatic enzymes, which can lead to Vitamin K deficiency in the newborn; hence, Vitamin K prophylaxis is essential at birth. 4. **Monotherapy:** The gold standard for managing epilepsy in pregnancy is to use the **lowest effective dose** of a **single drug** (monotherapy).

Question 478: What is the most serious side effect of valproate?

A. Fulminant hepatitis (Correct Answer)
B. Spina bifida
C. Weight gain
D. Thrombocytopenia

Explanation: **Explanation:** **Valproate** is a broad-spectrum antiepileptic drug with a complex mechanism of action, primarily involving the enhancement of GABAergic transmission and inhibition of sodium and calcium channels. **1. Why Fulminant Hepatitis is the correct answer:** While valproate has several adverse effects, **fulminant hepatic failure** is considered the most serious and life-threatening. It is an idiosyncratic reaction (not dose-dependent) that typically occurs within the first six months of therapy. The risk is highest in children under two years of age, especially those on polytherapy or with underlying metabolic disorders. It is characterized by a sudden onset of jaundice, coagulopathy, and encephalopathy. **2. Analysis of Incorrect Options:** * **B. Spina bifida:** This is a major **teratogenic** effect (Neural Tube Defect). While grave, it is a risk to the fetus rather than a direct "side effect" on the patient themselves. Valproate carries the highest risk of teratogenicity among all AEDs. * **C. Weight gain:** This is a very **common** side effect, often leading to poor compliance, but it is not considered "serious" or life-threatening. * **D. Thrombocytopenia:** This is a common **hematological** side effect (dose-related). While it requires monitoring, it rarely leads to fatal hemorrhage compared to the severity of fulminant hepatitis. **High-Yield Clinical Pearls for NEET-PG:** * **Mnemonic for Valproate side effects (VALPROATE):** **V**omiting, **A**lopecia (curly hair), **L**iver toxicity, **P**ancreatitis (acute/hemorrhagic), **R**etention of weight (gain), **O**edema, **A**ppetite increase, **T**eratogenicity (Spina Bifida), **E**nzyme inhibitor (unlike most AEDs which are inducers). * **Drug of Choice:** Valproate is the first-line treatment for Generalized Tonic-Clonic Seizures (GTCS), Myoclonic seizures, and Absence seizures. * **Monitoring:** Liver Function Tests (LFTs) are mandatory during the first 6 months of treatment.

Question 479: Which of the following conditions respond well with clonidine?

A. Opiate withdrawal
B. Attention-deficit/hyperactivity disorder
C. Tourette's disorder
D. All of the above (Correct Answer)

Explanation: **Explanation:** Clonidine is a centrally acting **$\alpha_2$-adrenergic agonist**. By stimulating presynaptic $\alpha_2$ receptors in the brainstem (specifically the vasomotor center and locus coeruleus), it reduces sympathetic outflow, leading to a decrease in peripheral resistance and heart rate. Beyond its use as an antihypertensive, its ability to modulate catecholamine release makes it effective in several neuropsychiatric conditions. * **Opiate Withdrawal:** Clonidine suppresses the sympathetic overactivity (tachycardia, hypertension, sweating, and anxiety) caused by the "noradrenergic storm" that occurs during opioid withdrawal. It is a standard non-opioid treatment for managing these autonomic symptoms. * **Attention-Deficit/Hyperactivity Disorder (ADHD):** It is used as a second-line or adjunctive treatment, particularly in children who do not tolerate stimulants or have comorbid tics. It works by modulating prefrontal cortex activity. * **Tourette’s Disorder:** Clonidine (and Guanfacine) are often preferred initial treatments for tics because they have a better side-effect profile compared to antipsychotics (haloperidol/pimozide). **Clinical Pearls for NEET-PG:** 1. **Rebound Hypertension:** Sudden withdrawal of clonidine can cause a hypertensive crisis due to a massive surge in catecholamines. 2. **Guanfacine:** A more selective $\alpha_{2A}$ agonist than clonidine, often preferred in ADHD due to less sedation and longer duration of action. 3. **Other Uses:** Clonidine is also used in the prophylaxis of **migraine**, treatment of **menopausal hot flashes**, and as a diagnostic test for **pheochromocytoma** (Clonidine Suppression Test). 4. **Side Effects:** Most common are sedation, xerostomia (dry mouth), and bradycardia.

Question 480: In a patient receiving a ketogenic diet for epilepsy, which one of the following antiepileptic agents should be avoided?

A. Sodium valproate (Correct Answer)
B. Phenytoin
C. Carbamazepine
D. Lamotrigine

Explanation: ### Explanation **Correct Option: A (Sodium Valproate)** The ketogenic diet (KD) is a high-fat, low-carbohydrate, and adequate-protein diet used for refractory epilepsy. It works by forcing the body to burn fats rather than carbohydrates, leading to the production of ketone bodies. **Sodium Valproate** must be avoided or used with extreme caution in patients on a ketogenic diet due to the following reasons: 1. **Inhibition of Fatty Acid Oxidation:** Valproate inhibits mitochondrial $\beta$-oxidation of fatty acids. Since the ketogenic diet relies entirely on fat metabolism for energy, Valproate can precipitate a metabolic crisis. 2. **Carnitine Depletion:** Valproate causes secondary carnitine deficiency. Carnitine is essential for transporting long-chain fatty acids into the mitochondria. The combination of KD and Valproate significantly increases the risk of **hepatotoxicity** and **hyperammonemic encephalopathy**. **Why other options are incorrect:** * **B, C, and D (Phenytoin, Carbamazepine, Lamotrigine):** These drugs do not significantly interfere with fatty acid metabolism or mitochondrial function. While they may have other side effects, they do not pose the specific metabolic contraindication seen with Valproate in the context of a ketogenic diet. **High-Yield Clinical Pearls for NEET-PG:** * **Topiramate and Zonisamide:** These should also be used cautiously with a ketogenic diet because both are carbonic anhydrase inhibitors. Since the ketogenic diet induces metabolic acidosis, the combination increases the risk of **nephrolithiasis** (kidney stones). * **Valproate Side Effects (Mnemonic: VALPROATE):** **V**omit, **A**lopecia, **L**iver toxicity, **P**ancreatitis/Platelets low, **R**etention of weight (gain), **O**edema, **A**taxia, **T**eratogenicity (Neural tube defects), **E**nzyme inhibitor. * **Drug of Choice:** Valproate remains the drug of choice for Generalized Tonic-Clonic Seizures (GTCS) and Myoclonic seizures, but it is strictly contraindicated in **Urea Cycle Disorders** and **Mitochondrial Disorders** (e.g., Alpers’ disease).

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