Central Nervous System Pharmacology Practice Questions

Q: Which of the following drugs is NOT used in the prophylactic management of migraine?

Levetiracetam. The prophylactic management of migraine aims to reduce the frequency, severity, and duration of attacks [2]. While several classes of drugs are effective, **Levetiracetam (Option D)** is the correct answer because it has not shown consistent clinical efficacy in migraine prophylaxis and is not recommended by major guidelines (AHS/AAN) [1]. **Why the other options are incorrect (Used in Prophylaxis):** * **Propranolol (Option A):** A non-selective beta-blocker and the **first-line drug** for migraine prophylaxis. It works by modulating central neurotransmitters and preventing vasodilation [2]. * **Flunarizine (Option B):** A non-selective calcium channel blocker with additional H1-blocking properties. It is highly effective in reducing attack frequency, though it may cause weight gain and sedation [2]. * **Topiramate (Option C):** An antiepileptic drug that acts by blocking voltage-gated sodium channels and enhancing GABAergic inhibition [1]. It is a **first-line** prophylactic agent, particularly useful in patients with comorbid obesity (due to weight loss side effects) [2]. **High-Yield Clinical Pearls for NEET-PG:** * **First-line Prophylactic Agents:** Beta-blockers (Propranolol, Timolol), Anticonvulsants (Topiramate, Valproate), and Tricyclic Antidepressants (Amitriptyline) [2]. * **Drug of Choice for Acute Attack:** Sumatriptan (5-HT 1B/1D agonist) [2]. * **Newer Agents:** **CGRP Antagonists** (e.g., Erenumab) are used for refractory cases [2]. * **Contraindication:** Avoid Propranolol in patients with bronchial asthma or peripheral vascular disease. Avoid Valproate in women of childbearing age due to teratogenicity [2].

Q: Methadone is used for opioid withdrawal because it functions as:

An agonist at the opioid receptor. **Explanation:** **1. Why Option C is Correct:** Methadone is a **long-acting synthetic μ (mu) opioid receptor agonist**. In the management of opioid use disorder, it is used for "Opioid Substitution Therapy" (OST). Because it is a full agonist with a long half-life (24–36 hours), it achieves two main goals: * **Prevents Withdrawal:** It stimulates the receptors enough to prevent the physical symptoms of withdrawal. * **Suppresses Craving:** It maintains a steady state in the blood, preventing the "rush" associated with heroin while blocking the cravings. **2. Why Other Options are Incorrect:** * **Option A (Antagonist):** Drugs like **Naloxone** and **Naltrexone** are antagonists. They block the receptor completely. Giving an antagonist to a dependent patient would precipitate immediate, severe withdrawal. * **Option B (Partial Antagonist):** This is not a standard pharmacological classification for opioid therapy. * **Option D (Partial Agonist):** **Buprenorphine** is the classic example of a partial μ-agonist. While it is also used for withdrawal, Methadone is distinct because it is a full agonist. **3. NEET-PG High-Yield Clinical Pearls:** * **NMDA Antagonism:** Apart from being a μ-agonist, Methadone also acts as an **NMDA receptor antagonist**, which may help in treating neuropathic pain and preventing opioid tolerance. * **Side Effect:** A critical "must-know" side effect of Methadone is **QT interval prolongation**, which can lead to Torsades de Pointes. * **Metabolism:** It is primarily metabolized by **CYP3A4**; therefore, inhibitors of this enzyme can lead to methadone toxicity. * **Gold Standard:** Methadone remains the gold standard for opioid maintenance therapy during **pregnancy**.

Q: What is the role of sodium metabisulfite in local anesthetic agents?

Reducing agent. **Explanation:** **Sodium metabisulfite** is added to local anesthetic (LA) solutions specifically when they contain a **vasoconstrictor** (like Adrenaline/Epinephrine). 1. **Why it is a Reducing Agent (Correct Answer):** Adrenaline is highly unstable and prone to oxidation, which turns the solution brown and renders the vasoconstrictor ineffective. Sodium metabisulfite acts as an **antioxidant (reducing agent)**. It has a higher affinity for oxygen than adrenaline; thus, it gets oxidized first, preventing the degradation of the catecholamine and extending the shelf life of the solution. 2. **Analysis of Incorrect Options:** * **Preservative:** While it "preserves" the adrenaline, in pharmacological terms, preservatives refer to antimicrobial agents. Examples in LA include **Methylparaben**, which prevents bacterial growth in multi-dose vials. * **Fungicide:** These are agents that kill fungi. Sodium metabisulfite does not serve this primary purpose in LA solutions. * **Vasoconstrictor:** The vasoconstrictor is the **Adrenaline** itself. Sodium metabisulfite is merely the stabilizer for it. **High-Yield Clinical Pearls for NEET-PG:** * **The "Sulfite" Allergy:** Patients with a history of "sulfite sensitivity" (common in asthmatics) may react to LA solutions containing adrenaline due to the sodium metabisulfite. In such cases, use **plain LA** (e.g., plain Lignocaine). * **pH Alteration:** The addition of sodium metabisulfite makes the LA solution more **acidic** (pH ~3.5–4.5 vs. ~6.5 for plain solutions). This can increase the "sting" on injection and slightly delay the onset of action. * **Methylparaben Warning:** Avoid using LA containing methylparaben for **spinal/epidural** anesthesia, as it is neurotoxic.

Q: Which is a gender-specific adverse effect of valproate?

Polycystic ovary syndrome (PCOS). Explanation:Sodium Valproate is a broad-spectrum antiepileptic drug with a unique side-effect profile. The correct answer is Polycystic Ovary Syndrome (PCOS) because it is the only option listed that is physiologically restricted to females.1. Why PCOS is the correct answer: Valproate is associated with reproductive endocrine dysfunction in women. It can cause hyperandrogenism, menstrual irregularities, and polycystic changes in the ovaries. The mechanism involves valproate-induced weight gain and insulin resistance, which increases androgen production from the theca cells. It may also directly inhibit the conversion of testosterone to estradiol.2. Why other options are incorrect: Weight gain: This is a very common side effect of valproate (due to increased appetite), but it occurs in both males and females. Alopecia: Valproate causes transient hair thinning or curling in about 10% of patients regardless of gender. Hepatotoxicity: This is a serious, idiosyncratic metabolic complication (more common in children <2 years) that affects both genders equally.NEET-PG High-Yield Pearls: Teratogenicity: Valproate is highly teratogenic, specifically causing Neural Tube Defects (e.g., Spina Bifida) due to interference with folate metabolism. Mnemonic for Valproate Side Effects (VALPROATE): Vomiting, Alopecia, Liver toxicity, Pancreatitis/PCOS, Retention of weight (Weight gain), Oedema, Ataxia, Teratogenicity/Thrombocytopenia, Encephalopathy (Hyperammonemia). Drug of Choice: It remains the drug of choice for Myoclonic seizures and Generalized Tonic-Clonic Seizures (GTCS).

Q: All of the following antiepileptic drugs can lead to weight loss except?

Valproate. **Explanation:** The correct answer is **Valproate (Option B)**. In pharmacological management of epilepsy, weight changes are a significant side effect that influences drug selection. **1. Why Valproate is the correct answer:** Valproate is notorious for causing **weight gain**, not weight loss. The mechanism is multifactorial, involving increased appetite, hyperinsulinemia, and metabolic changes. It is often avoided in patients who are already obese or have Polycystic Ovary Syndrome (PCOS), as it can exacerbate weight gain and hormonal imbalances. **2. Analysis of other options (Weight Loss inducing AEDs):** * **Topiramate (Option D):** This is the most potent antiepileptic associated with weight loss. It acts by inhibiting carbonic anhydrase and altering taste perception (making carbonated drinks taste "flat"), leading to reduced caloric intake. It is even FDA-approved in combination with Phentermine for weight loss. * **Zonisamide (Option C):** Similar to Topiramate, it is a sulfonamide derivative that causes significant weight loss and anorexia. * **Felbamate (Option A):** This drug is frequently associated with weight loss and anorexia, though its use is limited due to risks of aplastic anemia and hepatic failure. **High-Yield NEET-PG Pearls:** * **Weight Gain AEDs:** Valproate, Vigabatrin, Gabapentin, Pregabalin, and Carbamazepine. * **Weight Loss AEDs:** Topiramate, Zonisamide, and Felbamate. * **Weight Neutral AEDs:** Levetiracetam, Lamotrigine, and Phenytoin. * **Mnemonic for Topiramate side effects:** **"STOPS"** (Sedation, Stones [Kidney], Thinness [Weight loss], Ocular [Glaucoma], Paresthesia, Speech problems).

Q: Phenytoin is most widely used for which of the following conditions?

All of the above. **Explanation:** Phenytoin is a versatile hydantoin derivative that acts primarily by blocking **voltage-gated sodium channels** in their inactivated state. This stabilizes neuronal membranes and prevents the high-frequency repetitive firing of action potentials, making it effective across several neurological conditions. * **Grand mal epilepsy (Generalized Tonic-Clonic Seizures):** Phenytoin is a first-line traditional drug for GTCS. It inhibits the spread of seizure activity without causing significant sedation. * **Status Epilepticus:** Intravenous (IV) phenytoin (or its prodrug, **Fosphenytoin**) is a standard second-line treatment used to prevent the recurrence of seizures after the acute episode has been controlled by benzodiazepines (like Lorazepam). * **Trigeminal Neuralgia:** While Carbamazepine is the drug of choice, Phenytoin is an effective alternative for patients who do not tolerate Carbamazepine or fail to respond to it. It works by reducing the paroxysmal discharges in the trigeminal nerve. **High-Yield NEET-PG Pearls:** 1. **Kinetics:** Phenytoin follows **Zero-order kinetics** (capacity-limited elimination) at therapeutic or high doses, meaning small dose increases can lead to disproportionate rises in plasma levels (toxicity). 2. **Side Effects (Mnemonic: HOT MALARIA):** **H**irsutism, **O**steomalacia, **T**eratogenicity (Fetal Hydantoin Syndrome), **M**egaloblastic anemia (folate deficiency), **A**taxia, **L**ymphadenopathy, **I**nsulin inhibition (hyperglycemia), **R**igidity, and **A**rrhythmias (when given rapid IV). 3. **Gingival Hyperplasia:** A classic side effect caused by overgrowth of gum tissue due to increased platelet-derived growth factor (PDGF). 4. **Fosphenytoin:** Preferred over Phenytoin for IV use as it is water-soluble, has a neutral pH, and does not cause "Purple Glove Syndrome."

Q: What is the new drug approved for the treatment of tardive dyskinesia?

Valbenazine. **Explanation:** **Valbenazine** is the first drug specifically FDA-approved for the treatment of **Tardive Dyskinesia (TD)**. TD is a movement disorder caused by long-term use of dopamine receptor blockers (antipsychotics), characterized by upregulation of dopamine receptors. Valbenazine acts as a highly selective **Vesicular Monoamine Transporter 2 (VMAT2) inhibitor**. By inhibiting VMAT2, it prevents the packaging of dopamine into presynaptic vesicles, thereby reducing dopamine release into the synaptic cleft and alleviating the hyperkinetic movements of TD. **Analysis of Options:** * **Safinamide (Option A):** This is a reversible MAO-B inhibitor used as an add-on treatment for Parkinson’s disease to manage "off" episodes. It has no role in treating TD. * **Tetrabenazine (Option B):** While it is a VMAT2 inhibitor used for Huntington’s Chorea, it is not specifically preferred for TD due to its short half-life and significant side effects like depression and parkinsonism. * **Deutetrabenazine (Option D):** This is a deuterated form of tetrabenazine. While it is also approved for TD, **Valbenazine** is often highlighted in exams as the "first" or "novel" specific agent with a superior pharmacokinetic profile (once-daily dosing and less risk of depression). **High-Yield Clinical Pearls for NEET-PG:** 1. **VMAT2 Inhibitors:** Valbenazine and Deutetrabenazine are the current drugs of choice for TD. 2. **Mechanism:** They decrease dopamine levels without blocking the D2 receptor directly, avoiding the worsening of TD. 3. **Historical Context:** Previously, Vitamin E and Benzodiazepines were used, but they lacked robust efficacy. 4. **Pro-tip:** If a patient develops TD, the first step is to taper/stop the offending antipsychotic or switch to **Clozapine** (the antipsychotic with the lowest risk of TD).

Question 1

What is the primary mechanism of action of local anesthetics?

Accepted Answer

Inhibition of Na+ channels

Answer

Inhibition of Na+ K+ ATPase

Answer

Inhibition of K+ channels

Answer

Inhibition of Ca2+ channels

Question 2

Which of the following drugs is NOT used in the prophylactic management of migraine?

Accepted Answer

Levetiracetam

Answer

Propranolol

Answer

Flunarizine

Answer

Topiramate

Question 3

Methadone is used for opioid withdrawal because it functions as:

Accepted Answer

An agonist at the opioid receptor

Answer

An antagonist at the opioid receptor

Answer

A partial antagonist at the opioid receptor

Answer

A partial agonist at the opioid receptor

Question 4

Which of the following local anesthetics are not vasodilators?

Accepted Answer

Lignocaine

Answer

Bupivacaine

Answer

Benzocaine

Answer

Tetracaine

Question 5

What is the role of sodium metabisulfite in local anesthetic agents?

Accepted Answer

Reducing agent

Answer

Preservative

Answer

Fungicide

Answer

Vasoconstrictor

Question 6

Which is a gender-specific adverse effect of valproate?

Accepted Answer

Polycystic ovary syndrome (PCOS)

Answer

Weight gain

Answer

Alopecia

Answer

Hepatotoxicity

Question 7

All of the following antiepileptic drugs can lead to weight loss except?

Accepted Answer

Valproate

Answer

Felbamate

Answer

Zonisamide

Answer

Topiramate

Question 8

Phenytoin is most widely used for which of the following conditions?

Accepted Answer

All of the above

Answer

Grand mal epilepsy

Answer

Status epilepsy

Answer

Trigeminal neuralgia

Question 9

What is the new drug approved for the treatment of tardive dyskinesia?

Accepted Answer

Valbenazine

Answer

Safinamide

Answer

Tetrabenazine

Answer

Deutetrabenazine

Question 10

Local anesthetics act by:

Accepted Answer

Blocking voltage-gated sodium channels

Answer

Blocking voltage-gated calcium channels

Answer

Blocking voltage-gated potassium channels

Answer

Blocking voltage-gated chloride channels

Central Nervous System Pharmacology — MCQs

Central Nervous System Pharmacology — MCQs

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