Central Nervous System Pharmacology — MCQs

Central Nervous System Pharmacology Indian Medical PG Practice Questions and MCQs

Question 281: What is the most effective non-habit forming sedative?

A. Lorazepam
B. Zolpidem (Correct Answer)
C. Flurazepam
D. Trazodone

Explanation: **Explanation:** **Zolpidem** is the correct answer because it belongs to the "Z-drugs" (Non-benzodiazepine hypnotics), which are currently the first-line treatment for short-term insomnia. **Why Zolpidem is correct:** Unlike traditional Benzodiazepines (BZDs), Zolpidem is a selective agonist at the **α1 subunit** of the GABA-A receptor (BZ1 site). This selectivity provides potent sedative and hypnotic effects while lacking significant anticonvulsant, muscle relaxant, or anxiolytic properties. Crucially, Zolpidem has a **lower potential for tolerance, dependence, and "hangover" effects** compared to BZDs, making it the preferred "non-habit forming" option in clinical practice. **Why other options are incorrect:** * **Lorazepam (A) & Flurazepam (C):** These are classic Benzodiazepines. They bind non-selectively to various GABA-A subunits (α1, α2, α3, α5). This lack of selectivity leads to a higher risk of physical dependence, cognitive impairment, and significant withdrawal symptoms upon discontinuation. * **Trazodone (D):** While often used off-label for insomnia due to its sedative side effects (H1 and α1 blockade), it is primarily an antidepressant (SARI). It is not as effective as Zolpidem for sleep induction and is associated with side effects like priapism and orthostatic hypotension. **High-Yield Clinical Pearls for NEET-PG:** * **Antidote:** Flumazenil reverses the effects of both BZDs and Z-drugs (Zolpidem, Zaleplon, Eszopiclone). * **Zaleplon:** Has the shortest half-life among Z-drugs; ideal for sleep-onset insomnia. * **Eszopiclone:** The only Z-drug approved for long-term use (up to 6 months). * **Melatonin Agonist:** Ramelteon is another non-habit forming option, specifically acting on MT1 and MT2 receptors in the suprachiasmatic nucleus.

Question 282: What is the drug of choice in the treatment of infantile spasms?

A. ACTH (Correct Answer)
B. Phenobarbitone
C. Carbamazepine
D. Phenytoin

Explanation: **Explanation:** **Infantile Spasms (West Syndrome)** is characterized by a triad of infantile spasms, developmental regression, and a highly disorganized EEG pattern known as **hypsarrhythmia**. **1. Why ACTH is the Correct Answer:** Adrenocorticotropic Hormone (ACTH) is considered the first-line drug of choice for infantile spasms. While its exact mechanism is not fully understood, it is believed to suppress the overproduction of Corticotropin-Releasing Hormone (CRH), which acts as an excitatory neuropeptide in the developing brain. ACTH is highly effective in both stopping the spasms and resolving the hypsarrhythmia on EEG. **2. Why Other Options are Incorrect:** * **Phenobarbitone:** While used for neonatal seizures, it is ineffective for the specific pathophysiology of West Syndrome. * **Carbamazepine & Phenytoin:** These are sodium channel blockers used for focal or generalized tonic-clonic seizures. In the context of infantile spasms, they are not only ineffective but can occasionally **exacerbate** the condition. **3. Clinical Pearls for NEET-PG:** * **Vigabatrin:** This is the drug of choice specifically if infantile spasms are associated with **Tuberous Sclerosis**. Note that Vigabatrin carries a risk of permanent visual field defects. * **Second-line agents:** If ACTH or Vigabatrin fail, oral corticosteroids (Prednisolone) or Valproate may be considered. * **Ketogenic Diet:** Often used for refractory cases of infantile spasms. * **Key Side Effect of ACTH:** Monitor for hypertension, electrolyte imbalances, and increased risk of infections.

Question 283: Which of the following drugs is not an anticonvulsant?

A. Phenytoin
B. Flunarizine (Correct Answer)
C. Topiramate
D. Phenobarbitone

Explanation: ### Explanation The correct answer is **Flunarizine**. **1. Why Flunarizine is the correct answer:** Flunarizine is a **non-selective calcium channel blocker** with additional dopamine D2 receptor-blocking activity. While it is used clinically for the **prophylaxis of migraine** and the treatment of vertigo, it does not possess significant anticonvulsant properties. In fact, due to its dopamine-blocking effects, it can occasionally cause extrapyramidal side effects (like parkinsonism), which is a high-yield distinction from traditional anti-epileptic drugs (AEDs). **2. Why the other options are incorrect:** * **Phenytoin (Option A):** A classic hydantoin derivative and a first-line AED. It works by blocking voltage-gated sodium channels in their inactivated state, preventing high-frequency repetitive firing of neurons. * **Topiramate (Option C):** A broad-spectrum AED with multiple mechanisms: it blocks sodium channels, enhances GABA-A activity, and antagonizes kainate/AMPA glutamate receptors. It is used for both epilepsy and migraine prophylaxis. * **Phenobarbitone (Option D):** A long-acting barbiturate that acts as a GABA-A receptor modulator (increasing the duration of chloride channel opening). It is a primary drug for generalized tonic-clonic seizures and status epilepticus. **3. NEET-PG Clinical Pearls:** * **Migraine vs. Epilepsy:** While drugs like **Topiramate** and **Valproate** are used for both migraine prophylaxis and epilepsy, **Flunarizine** is strictly for migraine/vertigo and is *not* an AED. * **Phenytoin Side Effects:** Remember the mnemonic **"HOT MALARIA"** (Hirsutism, Osteomalacia, Teratogenicity, Megaloblastic anemia, Ataxia, Lymphadenopathy, Insulin inhibition, and Adenopathy/Gum Hyperplasia). * **Drug of Choice:** Phenobarbitone remains the drug of choice for neonatal seizures.

Question 284: What is the first-line treatment for trigeminal neuralgia?

A. Neurectomy
B. Carbamazepine (Correct Answer)
C. Regional nerve block
D. Radiofrequency

Explanation: **Explanation:** **Trigeminal Neuralgia (Tic Douloureux)** is characterized by sudden, severe, brief, stabbing, or shock-like recurrent pain in the distribution of one or more branches of the fifth cranial nerve. **Why Carbamazepine is the Correct Answer:** **Carbamazepine** is the **drug of choice (DOC)** and the first-line treatment for trigeminal neuralgia. It acts by blocking **use-dependent voltage-gated sodium channels**, which stabilizes neuronal membranes and inhibits the repetitive firing of the trigeminal nerve. It provides significant pain relief in approximately 70-80% of patients. **Why Other Options are Incorrect:** * **A. Neurectomy:** This is a destructive surgical procedure involving the cutting of the nerve. It is considered only when medical management fails and less invasive surgical options are exhausted. * **C. Regional nerve block:** While it can provide temporary relief, it is not a first-line or long-term management strategy. * **D. Radiofrequency (Rhizotomy):** This is a minimally invasive surgical option (thermal ablation of the nerve root). It is indicated only for patients who are refractory to medical therapy or cannot tolerate the side effects of drugs. **High-Yield Clinical Pearls for NEET-PG:** * **Second-line drugs:** Oxcarbazepine (often preferred due to fewer side effects), Baclofen, or Lamotrigine. * **Surgical DOC:** **Microvascular Decompression (MVD)**, also known as the Jannetta procedure, is the most effective surgical treatment for cases caused by vascular compression. * **Carbamazepine Side Effects:** Diplopia, ataxia, and most importantly, **Stevens-Johnson Syndrome (SJS)**, especially in patients with the **HLA-B*1502** allele. It is also a potent hepatic enzyme inducer. * **Monitoring:** Periodic CBC is required due to the risk of **agranulocytosis** and aplastic anemia.

Question 285: All of the following are adverse effects of naloxone in the treatment of opioid poisoning, except:

A. Hypertension
B. Pulmonary edema
C. Seizures (Correct Answer)
D. Ventricular dysrhythmia

Explanation: **Explanation:** **Naloxone** is a competitive opioid antagonist used as the drug of choice for acute opioid overdose. It works by displacing opioids from $\mu$, $\kappa$, and $\delta$ receptors. **Why Seizures is the Correct Answer:** Naloxone itself does **not** cause seizures. In fact, in the context of opioid toxicity, seizures are more commonly associated with specific opioids (like Meperidine/Pethidine due to its metabolite normeperidine or Tramadol) rather than the antagonist used to treat them. While naloxone precipitates acute withdrawal, the withdrawal syndrome from pure opioids (unlike alcohol or benzodiazepines) is physically distressing but typically **not life-threatening** and does not characteristically include seizures. **Analysis of Incorrect Options (Adverse Effects of Naloxone):** The primary adverse effects of naloxone are due to the **sudden reversal of opioid effects** and the subsequent massive surge in catecholamines (sympathetic overdrive): * **Hypertension & Ventricular Dysrhythmia (Options A & D):** The rapid reversal of opioid-induced CNS depression leads to a "catecholamine storm," causing tachycardia, severe hypertension, and potentially fatal cardiac arrhythmias. * **Pulmonary Edema (Option B):** Non-cardiogenic pulmonary edema is a well-documented, rare, but severe complication of rapid naloxone administration, thought to be mediated by the sudden shift in hemodynamics and increased pulmonary capillary permeability. **NEET-PG High-Yield Pearls:** * **Half-life:** Naloxone has a very short half-life (30–90 mins). Since many opioids (like Methadone) last longer, patients must be monitored for **re-narcotization** (re-sedation). * **Route:** It is poorly absorbed orally due to high first-pass metabolism; it is given IV, IM, or intranasally. * **Naltrexone:** Unlike naloxone, naltrexone is orally active and long-acting, used for maintenance therapy in opioid de-addiction and alcohol dependence.

Question 286: Which of the following drugs is NOT used in the prophylactic management of migraine?

A. Propranolol
B. Flunarizine
C. Topiramate
D. Levetiracetam (Correct Answer)

Explanation: 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].

Question 287: Which of the following is a short-acting non-depolarizing muscle relaxant?

A. Mivacurium (Correct Answer)
B. Vecuronium
C. Atracurium
D. Succinylcholine

Explanation: **Explanation:** Neuromuscular blocking agents (NMBAs) are classified based on their mechanism of action (Depolarizing vs. Non-depolarizing) and their **duration of action**. **1. Why Mivacurium is correct:** Mivacurium is a benzylisoquinoline derivative and is the only **short-acting** non-depolarizing muscle relaxant (duration: 12–18 minutes). Like Succinylcholine, it is metabolized by **plasma pseudocholinesterase**, which accounts for its rapid offset. **2. Why the other options are incorrect:** * **Vecuronium:** This is an aminosteroid NMBA with an **intermediate duration** of action (30–40 minutes). It is primarily excreted via the bile and kidneys. * **Atracurium:** This is a benzylisoquinoline NMBA with an **intermediate duration** of action (30–45 minutes). It is unique because it undergoes **Hofmann elimination** (spontaneous degradation at body pH and temperature), making it safe in liver and kidney failure. * **Succinylcholine:** While it is short-acting (5–10 minutes), it is a **depolarizing** muscle relaxant. The question specifically asks for a *non-depolarizing* agent. **High-Yield Clinical Pearls for NEET-PG:** * **Shortest acting NMBA:** Succinylcholine (Depolarizing); Mivacurium (Non-depolarizing). * **Longest acting NMBA:** Gallamine or Pancuronium. * **Hofmann Elimination:** Seen with Atracurium and Cisatracurium (Drug of choice in renal/hepatic failure). * **Adverse Effect of Mivacurium:** It can cause significant **histamine release**, leading to hypotension and flushing if injected rapidly. * **Pseudocholinesterase Deficiency:** Patients with this genetic condition will experience prolonged apnea after receiving Mivacurium or Succinylcholine.

Question 288: Which of the following diuretics decreases the renal lithium clearance?

A. Acetazolamide
B. Mannitol
C. Furosemide (Correct Answer)
D. Spironolactone

Explanation: **Explanation:** The correct answer is **Furosemide (Option C)**. **Mechanism of Interaction:** Lithium is handled by the kidneys similarly to sodium. It is filtered at the glomerulus and reabsorbed (about 80%) in the proximal convoluted tubule (PCT). When diuretics like **Furosemide** (Loop diuretic) or **Thiazides** cause sodium and water depletion, the body compensates by increasing sodium reabsorption in the PCT. Since the renal tubules cannot distinguish well between sodium and lithium ions, **lithium reabsorption is also increased**. This leads to a **decrease in renal lithium clearance**, resulting in elevated serum lithium levels and a high risk of lithium toxicity. **Analysis of Incorrect Options:** * **A. Acetazolamide:** This is a carbonic anhydrase inhibitor. It actually **increases** lithium excretion (increases clearance) by interfering with its reabsorption in the PCT. * **B. Mannitol:** As an osmotic diuretic, it increases the flow of tubular fluid and inhibits the reabsorption of electrolytes and water throughout the nephron, thereby **increasing** lithium clearance. * **C. Spironolactone:** While potassium-sparing diuretics have a lesser effect on lithium compared to thiazides or loop diuretics, they generally do not significantly decrease clearance to the extent that Furosemide or Thiazides do. However, in the context of this question, Furosemide is the classic established cause of decreased clearance. **High-Yield Clinical Pearls for NEET-PG:** * **Thiazides** are the most notorious for causing lithium toxicity (more so than Loop diuretics). * **NSAIDs** (except Aspirin and Sulindac) and **ACE inhibitors/ARBs** also decrease lithium clearance and can precipitate toxicity. * **Lithium Toxicity Symptoms:** Coarse tremors, ataxia, dysarthria, seizures, and diabetes insipidus (nephrogenic). * **Management of Toxicity:** Hemodialysis is the treatment of choice for severe lithium poisoning.

Question 289: All of the following antiepileptic drugs can lead to weight loss except?

A. Felbamate
B. Valproate (Correct Answer)
C. Zonisamide
D. Topiramate

Explanation: **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).

Question 290: Phenytoin is most widely used for which of the following conditions?

A. Grand mal epilepsy
B. Status epilepsy
C. Trigeminal neuralgia
D. All of the above (Correct Answer)

Explanation: **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."

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General Anesthetics

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Local Anesthetics

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Sedative-Hypnotics

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Antiepileptic Drugs

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Antiparkinsonian Drugs

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Opioid Analgesics

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Drugs of Abuse and Addiction

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Psychostimulants

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Hallucinogens

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CNS Stimulants and Cognitive Enhancers

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