Central Nervous System Pharmacology — MCQs

Central Nervous System Pharmacology Indian Medical PG Practice Questions and MCQs

Question 351: Administration of which antiepileptic drug is associated with the development of hyperldnesia in children?

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

Explanation: **Explanation:** The correct answer is **Phenobarbitone**. **Mechanism and Rationale:** Phenobarbitone is a long-acting barbiturate that acts as a GABA-A receptor agonist, increasing the duration of chloride channel opening. While it is an effective anticonvulsant, it has a paradoxical effect on the behavior of children. Instead of sedation, it frequently causes **behavioral disturbances**, specifically **hyperkinesia** (hyperactivity), irritability, and decreased cognitive performance. This "paradoxical excitement" is a classic side effect often tested in exams. **Analysis of Incorrect Options:** * **Phenytoin sodium:** Primarily associated with gingival hyperplasia, hirsutism, and osteomalacia. In children, it can cause coarsening of facial features but not typically hyperkinesia. * **Sodium valproate:** Known for weight gain, alopecia, and hepatotoxicity. It is generally sedating rather than activating. * **Carbamazepine:** Common side effects include diplopia, ataxia, and hyponatremia (SIADH). It is rarely associated with hyperactivity in children. **High-Yield Clinical Pearls for NEET-PG:** * **Drug of Choice (DOC):** Phenobarbitone remains the DOC for **Neonatal Seizures**. * **Paradoxical Effect:** While it causes sedation in adults, it causes **hyperactivity/irritability in children** and **confusion/agitation in the elderly**. * **Metabolism:** It is a potent **microsomal enzyme inducer**, leading to numerous drug-drug interactions (e.g., reducing the efficacy of oral contraceptives or warfarin). * **Contraindication:** It is strictly contraindicated in patients with **Acute Intermittent Porphyria** as it induces ALA synthase.

Question 352: Secobarbitone is?

A. Long acting barbiturate
B. Intermediate acting barbiturate
C. Short acting barbiturate (Correct Answer)
D. Ultra short acting barbiturate

Explanation: **Explanation:** Barbiturates are classified primarily based on their **duration of action**, which is determined by their lipid solubility and the rate at which they are metabolized by the liver or redistributed from the brain. **1. Why the correct answer is right:** **Secobarbitone (and Pentobarbitone)** are classified as **Short-acting barbiturates**. They have a duration of action typically ranging from **3 to 6 hours**. These drugs are highly lipid-soluble, allowing for rapid onset, but are metabolized relatively quickly by the liver compared to long-acting variants. **2. Why the incorrect options are wrong:** * **Long-acting (12–24 hours):** This category includes **Phenobarbitone**. These have low lipid solubility and are primarily excreted unchanged by the kidneys. They are used mainly for seizure control (Epilepsy). * **Intermediate-acting (6–12 hours):** This category includes **Amobarbitone** and Butabarbital. Their duration falls between the short and long-acting agents. * **Ultra-short acting (< 30 minutes):** This category includes **Thiopentone sodium** and Methohexital. These are highly lipophilic drugs used for the induction of anesthesia. Their action is terminated by **redistribution** from the brain to fatty tissues, rather than metabolism. **High-Yield Clinical Pearls for NEET-PG:** * **Mechanism:** Barbiturates increase the **duration** of GABA-A receptor chloride channel opening (unlike Benzodiazepines, which increase *frequency*). * **Enzyme Induction:** Barbiturates are potent **microsomal enzyme inducers** (CYP450), leading to numerous drug interactions (e.g., decreasing the efficacy of Warfarin). * **Contraindication:** They are strictly contraindicated in **Acute Intermittent Porphyria** because they induce $\delta$-aminolevulinic acid (ALA) synthase, the rate-limiting enzyme in porphyrin synthesis. * **Antidote:** There is **no specific pharmacological antagonist** for barbiturate overdose; management is purely supportive (alkalinization of urine for Phenobarbitone).

Question 353: What are the contraindications of phenytoin?

A. Hirsutism
B. Hepatotoxicity
C. Osteomalacia
D. All the above (Correct Answer)

Explanation: **Explanation:** Phenytoin is a widely used antiepileptic drug (AED) known for its narrow therapeutic index and a distinct profile of side effects. The correct answer is **"All the above"** because the options listed represent significant adverse effects that serve as clinical contraindications or reasons for immediate discontinuation. 1. **Hirsutism (Option A):** Phenytoin causes excessive hair growth, particularly in females. While not life-threatening, it is a major cosmetic concern and a relative contraindication in young female patients, where alternatives like Levetiracetam are preferred. 2. **Hepatotoxicity (Option B):** Phenytoin is metabolized by the liver (CYP2C9/2C19). It can cause drug-induced liver injury (DILI) or hypersensitivity syndromes (DRESS). It is strictly contraindicated in patients with pre-existing hepatic impairment. 3. **Osteomalacia (Option C):** Phenytoin is a potent **inducer of Cytochrome P450 enzymes**. This leads to the increased metabolism of Vitamin D, resulting in hypocalcemia and secondary hyperparathyroidism, which manifests as osteomalacia (in adults) or rickets (in children). **High-Yield Clinical Pearls for NEET-PG:** * **Teratogenicity:** Phenytoin causes **Fetal Hydantoin Syndrome** (cleft lip/palate, digital hypoplasia). * **Kinetics:** It follows **Zero-order kinetics** (non-linear) at therapeutic/high concentrations; a small dose increase can lead to toxicity. * **Gingival Hyperplasia:** Caused by increased expression of platelet-derived growth factor (PDGF). * **Mnemonic for Side Effects (P-H-E-N-Y-T-O-I-N):** **P**-450 induction, **H**irsutism, **E**nlarged gums, **N**ystagmus, **Y**ellow-brown skin (pigmentation), **T**eratogenicity, **O**steomalacia, **I**nterference with B12/Folate (Megaloblastic anemia), **N**europathy.

Question 354: Which drug is effective in the treatment of Tardive dyskinesia?

A. Central anticholinergic
B. Dantrolene
C. Succinylcholine
D. Tetrabenazine (Correct Answer)

Explanation: **Explanation:** **Tardive Dyskinesia (TD)** is a late-onset extrapyramidal side effect caused by chronic use of dopamine receptor blockers (antipsychotics). It is characterized by involuntary, repetitive movements (e.g., lip-smacking, tongue protrusion) due to **dopamine receptor supersensitivity** in the nigrostriatal pathway. **Why Tetrabenazine is correct:** Tetrabenazine is a reversible inhibitor of the **Vesicular Monoamine Transporter 2 (VMAT2)**. By inhibiting VMAT2, it prevents the storage of dopamine in presynaptic vesicles, leading to dopamine depletion in the synaptic cleft. Reducing the amount of dopamine available to stimulate the supersensitive receptors effectively alleviates the involuntary movements of TD. (Note: Valbenazine and Deutetrabenazine are newer, more selective VMAT2 inhibitors). **Why the other options are incorrect:** * **A. Central anticholinergics (e.g., Benztropine, Trihexyphenidyl):** These are used to treat *acute* extrapyramidal symptoms like dystonia or parkinsonism. However, in TD, they can actually **worsen** symptoms by further shifting the dopamine-acetylcholine balance. * **B. Dantrolene:** This is a peripherally acting muscle relaxant (ryanodine receptor antagonist) used primarily for **Malignant Hyperthermia** and Neuroleptic Malignant Syndrome (NMS). * **C. Succinylcholine:** This is a depolarizing neuromuscular blocker used for rapid sequence induction in anesthesia; it has no role in chronic movement disorders. **High-Yield Clinical Pearls for NEET-PG:** * **Drug of Choice for TD:** VMAT2 inhibitors (Tetrabenazine/Valbenazine). * **Paradoxical Management:** The first step in TD management is often reducing the dose of the offending antipsychotic or switching to **Clozapine** (the antipsychotic with the lowest risk of TD). * **Tetrabenazine Side Effect:** It can cause significant depression and suicidality due to systemic depletion of serotonin and norepinephrine.

Question 355: Which of the following anti-epileptic agents is known to cause gingival hyperplasia as a reversible side-effect?

A. Ethosuximide
B. Phenobarbitone
C. Sodium valproate
D. None of the above (Correct Answer)

Explanation: **Explanation:** The correct answer is **None of the above** because the classic anti-epileptic drug associated with gingival hyperplasia is **Phenytoin**, which is not listed among the options. **1. Why the Correct Answer is Right:** Gingival hyperplasia (gum overgrowth) is a hallmark side effect of Phenytoin. It occurs due to the stimulation of alveolar fibroblasts and increased collagen production. Crucially, while the question describes it as a "reversible" side effect, in clinical practice, it is often only **partially reversible** upon drug discontinuation and frequently requires surgical intervention (gingivectomy) if oral hygiene is poor. Since Phenytoin is absent from the options, "None of the above" is the correct choice. **2. Analysis of Incorrect Options:** * **Ethosuximide:** This is the drug of choice for Absence seizures. Its primary side effects are GI distress, drowsiness, and rarely, Stevens-Johnson Syndrome, but not gingival hyperplasia. * **Phenobarbitone:** A barbiturate used for neonatal seizures and status epilepticus. Common side effects include sedation, behavioral changes in children, and osteomalacia, but not gum hypertrophy. * **Sodium Valproate:** A broad-spectrum agent. Its signature side effects include weight gain, alopecia (reversible), hepatotoxicity, and pancreatitis. It is also highly teratogenic (neural tube defects). **3. Clinical Pearls for NEET-PG:** * **Other drugs causing Gingival Hyperplasia:** Remember the mnemonic **"P-C-N"**: **P**henytoin, **C**alcium Channel Blockers (especially Nifedipine), and **N**ephrotoxic immunosuppressants (Cyclosporine). * **Phenytoin Side Effects (Mnemonic: HOT MALAYALAM):** **H**irsutism, **O**steomalacia, **T**eratogenicity (Fetal Hydantoin Syndrome), **M**egaloblastic anemia, **A**taxia, **L**ymphadenopathy, **A**rrhythmias, **Y**ellow-brown skin, **A**denopathy, **L**eukopenia, **A**ntifolate, and **M**outh (Gingival Hyperplasia).

Question 356: Which of the following statements regarding sumatriptan is WRONG?

A. It is a selective 5-HT1D/1B receptor agonist.
B. It is safe for use in patients with epilepsy. (Correct Answer)
C. It suppresses neurogenic inflammation of cranial blood vessels.
D. It is useful in the treatment of an acute attack of migraine.

Explanation: **Explanation:** Sumatriptan is the prototype of the "Triptan" class, which revolutionized the management of acute migraine. **Why Option B is the Correct (Wrong Statement):** Sumatriptan and other triptans are known to lower the seizure threshold. While not strictly contraindicated in all cases, they are **not considered "safe"** for patients with epilepsy as they can potentially trigger seizures. Therefore, they should be used with extreme caution, if at all, in patients with a known seizure disorder. **Analysis of Other Options:** * **Option A:** Sumatriptan is a selective agonist at **5-HT$_{1B}$ and 5-HT$_{1D}$** receptors. 5-HT$_{1B}$ receptors are primarily located on cranial blood vessels, while 5-HT$_{1D}$ receptors are located on trigeminal nerve terminals. * **Option C:** By stimulating pre-junctional 5-HT$_{1D}$ receptors, sumatriptan inhibits the release of pro-inflammatory neuropeptides (like CGRP and Substance P). This **suppresses neurogenic inflammation** and prevents plasma extravasation. * **Option D:** Sumatriptan is a first-line drug for the **abortive (acute) treatment** of moderate-to-severe migraine attacks. It is not used for prophylaxis. **NEET-PG High-Yield Pearls:** * **Mechanism of Action:** 1. Vasoconstriction of dilated cranial vessels (5-HT$_{1B}$); 2. Inhibition of dural neurogenic inflammation (5-HT$_{1D}$). * **Contraindications:** Since triptans cause vasoconstriction, they are strictly contraindicated in **Ischemic Heart Disease (Angina/MI)**, Peripheral Vascular Disease, and Uncontrolled Hypertension. * **Pharmacokinetics:** Sumatriptan has low oral bioavailability (~15%). Subcutaneous administration provides the fastest onset of action. * **Chest Symptoms:** "Triptan sensations" (tightness/pressure in the chest and throat) occur in ~15% of patients; these are usually due to esophageal vasospasm rather than cardiac ischemia.

Question 357: All of the following drugs are used in the treatment of dementia except?

A. Memantine
B. Duloxetine (Correct Answer)
C. Galantamine
D. Donepezil

Explanation: **Explanation:** The treatment of dementia, particularly Alzheimer’s disease, focuses on enhancing cholinergic transmission or modulating glutamatergic excitability. **Why Duloxetine is the correct answer:** **Duloxetine** is a **Serotonin-Norepinephrine Reuptake Inhibitor (SNRI)**. It is primarily used as an antidepressant, anxiolytic, and for the management of chronic pain conditions like diabetic peripheral neuropathy and fibromyalgia. It has **no established role** in the cognitive enhancement or pathophysiology of dementia. **Analysis of incorrect options:** * **Donepezil & Galantamine (Options C & D):** These are **Reversible Acetylcholinesterase Inhibitors (AChEIs)**. By inhibiting the breakdown of acetylcholine in the synaptic cleft, they compensate for the cholinergic deficit seen in Alzheimer’s. They are first-line treatments for mild-to-moderate dementia. (Note: Rivastigmine is another drug in this class). * **Memantine (Option A):** This is an **NMDA receptor antagonist**. It works by blocking pathological "noise" from excessive glutamate stimulation, which prevents excitotoxicity. It is typically used for moderate-to-severe Alzheimer’s, often in combination with Donepezil. **High-Yield Clinical Pearls for NEET-PG:** * **Rivastigmine** is the only AChEI available as a **transdermal patch**, which improves compliance and reduces GI side effects. * **Common Side Effects of AChEIs:** Diarrhea, nausea, and bradycardia (SLUDGE effects). * **Newer Drug:** **Aducanumab** and **Lecanemab** are monoclonal antibodies targeting amyloid-beta plaques, recently approved for early-stage Alzheimer's. * **Vascular Dementia:** Management focuses on controlling risk factors (Aspirin, Statins) rather than specific cognitive enhancers.

Question 358: Fetal hydantoin syndrome is seen if which of the following drugs is used in pregnancy?

A. Phenytoin (Correct Answer)
B. Alcohol
C. Ethosuximide
D. Phenobarbiton

Explanation: **Explanation:** **Phenytoin** is a well-known teratogen. When used during pregnancy, it can lead to a constellation of birth defects known as **Fetal Hydantoin Syndrome (FHS)**. The underlying mechanism involves the production of epoxide metabolites, which cause oxidative stress and interfere with folate metabolism during organogenesis. **Why Phenytoin is correct:** Fetal Hydantoin Syndrome is characterized by a specific tetrad of symptoms: 1. **Craniofacial abnormalities:** Cleft lip/palate and a broad nasal bridge. 2. **Hypoplasia of phalanges and nails:** (A very high-yield "distinguishing" feature). 3. **Growth retardation:** Both prenatal and postnatal. 4. **Mental retardation/Cognitive deficits.** **Why the other options are incorrect:** * **Alcohol:** Causes **Fetal Alcohol Syndrome (FAS)**, characterized by microcephaly, smooth philtrum, thin upper lip, and septal heart defects. * **Ethosuximide:** Primarily used for absence seizures; it is generally considered to have a lower teratogenic potential than phenytoin or valproate, though no AED is entirely risk-free. * **Phenobarbital:** Can cause "Fetal Phenobarbital Syndrome," which overlaps with FHS but is distinct. It is more commonly associated with neonatal withdrawal and vitamin K deficiency (hemorrhagic disease of the newborn). **NEET-PG High-Yield Pearls:** * **Valproate** is the *most* teratogenic AED, specifically linked to **Neural Tube Defects** (Spina Bifida) due to folate antagonism. * **Drug of choice** for epilepsy in pregnancy: **Lamotrigine** or **Levetiracetam** (safest profiles). * To prevent AED-induced hemorrhagic disease of the newborn, give **Vitamin K** to the mother in the last month of pregnancy and to the neonate at birth. * Always supplement **Folic acid (5mg/day)** in pregnant women taking any enzyme-inducing AEDs.

Question 359: Selective decrease in IgA is seen with administration of which of the following drugs?

A. Phenytoin (Correct Answer)
B. Diazepam
C. Clonazepam
D. Phenobarbitone

Explanation: **Explanation:** **Phenytoin** is a classic hydantoin anticonvulsant known for a unique side effect profile. The selective decrease in **Serum IgA** levels occurs in approximately 20–25% of patients treated with Phenytoin. The underlying mechanism involves the inhibition of B-cell differentiation into IgA-secreting plasma cells. While often asymptomatic, this can occasionally lead to an increased frequency of upper respiratory tract infections or contribute to the development of gingival hyperplasia. **Analysis of Options:** * **Phenytoin (Correct):** It is the only drug among the options consistently associated with selective IgA deficiency. It also causes other immunological effects like the DRESS syndrome and Stevens-Johnson Syndrome (SJS). * **Diazepam & Clonazepam (Incorrect):** These are Benzodiazepines (BZDs) that act via GABA-A receptors. They do not have significant effects on immunoglobulin levels or the humoral immune system. * **Phenobarbitone (Incorrect):** While it is a long-acting barbiturate used for epilepsy, it is not associated with selective IgA deficiency. Its primary side effects include sedation, cognitive impairment, and osteomalacia. **High-Yield Clinical Pearls for NEET-PG:** * **Mnemonic for Phenytoin Side Effects (HOT MALAI):** **H**irsutism, **O**steomalacia, **T**eratogenicity (Fetal Hydantoin Syndrome), **M**egaloblastic anemia (due to folate deficiency), **A**taxia, **L**ymphadenopathy, **A**rrhythmias (on rapid IV), **I**nsulin inhibition (hyperglycemia), and **Gingival Hyperplasia**. * Phenytoin follows **Zero-order kinetics** (Capacity-limited elimination) at therapeutic or high concentrations. * It is a potent **Inducer** of Cytochrome P450 enzymes.

Question 360: Phenytoin therapy may lead to which of the following?

A. Microcytic anemia
B. Thrombosis
C. Hypercalcemia
D. Folic acid deficiency (Correct Answer)

Explanation: **Explanation:** **Phenytoin** is a widely used hydantoin derivative for generalized tonic-clonic and partial seizures. The correct answer is **Folic acid deficiency** because phenytoin interferes with the absorption and metabolism of folate. 1. **Why Folic Acid Deficiency is Correct:** Phenytoin inhibits the enzyme **intestinal conjugase**, which is required to break down dietary polyglutamates into monoglutamates for absorption. Additionally, it may induce hepatic enzymes that accelerate folate catabolism. Long-term therapy leads to low serum folate levels in up to 50% of patients, occasionally manifesting as **Megaloblastic Anemia**. 2. **Why Other Options are Incorrect:** * **A. Microcytic anemia:** Phenytoin causes *macrocytic* (megaloblastic) anemia due to folate deficiency, not microcytic anemia (which is typically associated with iron deficiency). * **B. Thrombosis:** Phenytoin does not cause thrombosis. In fact, if used in neonates or during pregnancy (Fetal Hydantoin Syndrome), it can lead to a deficiency of Vitamin K-dependent clotting factors, increasing the risk of **hemorrhage**, not clotting. * **C. Hypercalcemia:** Phenytoin actually causes **Hypocalcemia** and osteomalacia. It induces cytochrome P450 enzymes, leading to increased catabolism of Vitamin D. **High-Yield Clinical Pearls for NEET-PG:** * **Mnemonic for Phenytoin Side Effects (HOT MALAI):** **H**irsutism, **O**steomalacia, **T**eratogenicity (Fetal Hydantoin Syndrome), **M**egaloblastic anemia, **A**taxia, **L**ymphadenopathy, **A**rrhythmias (on rapid IV injection), **I**nsulin inhibition (leading to hyperglycemia) and **G**ingival hyperplasia. * **Zero-Order Kinetics:** Phenytoin follows saturation kinetics; a small dose increase can lead to a disproportionate rise in plasma levels and toxicity. * **Drug of Choice:** Phenytoin is a first-line agent for Status Epilepticus (after Benzodiazepines).

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