Central Nervous System Pharmacology — MCQs

Central Nervous System Pharmacology Indian Medical PG Practice Questions and MCQs

Question 291: Which calcium channel blocker is specifically indicated to counteract cerebral vasospasm and neurological sequelae following subarachnoid hemorrhage?

A. Lacidipine
B. Nicardipine
C. Nimodipine (Correct Answer)
D. Nitrendipine

Explanation: **Explanation:** **Nimodipine** is the drug of choice for preventing and treating delayed cerebral ischemia (DCI) caused by **cerebral vasospasm** following an aneurysmal subarachnoid hemorrhage (SAH). **Why Nimodipine is correct:** Nimodipine is a second-generation dihydropyridine calcium channel blocker (CCB). Its clinical superiority in SAH is due to its **high lipid solubility**, which allows it to readily cross the blood-brain barrier. It acts by inhibiting the influx of calcium into vascular smooth muscle cells, thereby preventing the intense vasoconstriction (vasospasm) that typically occurs 4 to 14 days after a bleed. It also exerts a neuroprotective effect by limiting calcium-mediated neuronal damage. **Why the other options are incorrect:** * **Lacidipine:** A long-acting dihydropyridine used primarily for the management of systemic hypertension. It does not have a specific indication for cerebral vasospasm. * **Nicardipine:** While it is used intravenously for hypertensive emergencies and has some cerebral vasodilatory properties, it lacks the specific clinical evidence and preferential "cerebro-vascular" selectivity that Nimodipine possesses for SAH outcomes. * **Nitrendipine:** Primarily used as an antihypertensive agent; it does not achieve the necessary CNS concentrations to be effective for post-SAH vasospasm. **High-Yield Clinical Pearls for NEET-PG:** * **Route & Timing:** Nimodipine should be started within 96 hours of SAH onset and continued for 21 days. * **Administration:** It is typically given **orally** (or via nasogastric tube). If given IV, extreme caution is required to avoid severe hypotension. * **Drug Class:** All options belong to the **Dihydropyridine** class of CCBs, which primarily act on L-type calcium channels in the vasculature rather than the heart.

Question 292: An antiepileptic drug can also be used for the treatment of post-herpetic neuralgia and pain due to diabetic neuropathy. Which of the following can be this agent?

A. Carbamazepine
B. Gabapentin (Correct Answer)
C. Lamotrigine
D. Primidone

Explanation: **Explanation:** **Gabapentin** is the correct answer because it is a first-line agent for **neuropathic pain**, including post-herpetic neuralgia (PHN) and painful diabetic neuropathy. 1. **Mechanism of Action:** Despite being a structural analog of GABA, Gabapentin does not act on GABA receptors. Instead, it binds to the **$\alpha_2\delta$ subunit of voltage-gated calcium channels** in the CNS. This binding decreases the entry of calcium into presynaptic terminals, thereby reducing the release of excitatory neurotransmitters like glutamate and substance P, which effectively modulates pain signaling. 2. **Analysis of Incorrect Options:** * **Carbamazepine (A):** While it is an antiepileptic, it is the drug of choice for **Trigeminal Neuralgia**, not typically the first choice for PHN or diabetic neuropathy. * **Lamotrigine (C):** Used primarily for focal seizures, Lennox-Gastaut syndrome, and bipolar disorder. It is not a standard treatment for PHN. * **Primidone (D):** A prodrug converted to phenobarbital; it is used for essential tremors and seizures but has no role in neuropathic pain management. **High-Yield Clinical Pearls for NEET-PG:** * **Pregabalin** shares the same mechanism as Gabapentin but has higher bioavailability and potency. * **Drug of Choice (DOC) Summary:** * Trigeminal Neuralgia: **Carbamazepine** * Post-herpetic Neuralgia: **Gabapentin/Pregabalin** (or TCAs like Amitriptyline) * Diabetic Neuropathy: **Duloxetine** (SNRI), **Gabapentin**, or **Pregabalin**. * **Side Effects:** Gabapentin commonly causes sedation, dizziness, and peripheral edema. It is excreted unchanged by the kidneys, requiring dose adjustment in renal failure.

Question 293: Which foods should be avoided when a patient is taking Monoamine Oxidase Inhibitors (MAOIs)?

A. Cheese
B. Beer
C. Fish
D. All of the above (Correct Answer)

Explanation: ### Explanation The correct answer is **D. All of the above**. **The Underlying Concept: The "Cheese Reaction"** Monoamine Oxidase Inhibitors (MAOIs), such as Phenelzine or Tranylcypromine, inhibit the enzyme responsible for breaking down biogenic amines. **Tyramine** is an indirectly acting sympathomimetic amine found in fermented, aged, or processed foods. Normally, MAO-A in the gut and liver degrades dietary tyramine. When a patient takes a non-selective MAOI, this protective barrier is lost. Tyramine enters the systemic circulation and reaches the adrenergic nerve endings, where it displaces large amounts of stored norepinephrine into the synaptic cleft. This massive release of catecholamines leads to a **Hypertensive Crisis** (characterized by severe headache, palpitations, and potentially intracranial hemorrhage). **Analysis of Options:** * **A. Cheese:** Specifically aged cheeses (Cheddar, Swiss, Blue) are the classic culprits due to high tyramine content. * **B. Beer:** Fermented beverages, including tap beers and certain red wines (Chianti), contain significant tyramine. * **C. Fish:** While fresh fish is safe, dried, pickled, or smoked fish (like herring) are high-risk foods. **High-Yield Clinical Pearls for NEET-PG:** * **Drug of Choice for Hypertensive Crisis:** Phentolamine (non-selective alpha-blocker). * **The "Safe" MAOI:** **Moclobemide** (a RIMA – Reversible Inhibitor of MAO-A) is much less likely to cause the cheese reaction because it can be displaced by tyramine, allowing the enzyme to function. * **Avoid SSRIs:** Combining MAOIs with SSRIs can lead to **Serotonin Syndrome**; a "washout period" of 2 weeks (5 weeks for Fluoxetine) is mandatory when switching drugs. * **Other foods to avoid:** Yeast extracts (Marmite), soy sauce, and overripe bananas.

Question 294: Which of the following is true regarding benzodiazepines?

A. They alter sleep patterns more than other sedatives.
B. All benzodiazepines have pharmacologically active metabolites.
C. They induce liver enzymes.
D. At higher doses, they are less toxic than other sedatives. (Correct Answer)

Explanation: ### Explanation **Correct Option: D. At higher doses, they are less toxic than other sedatives.** Benzodiazepines (BZDs) have a high **therapeutic index** compared to older sedatives like barbiturates. This is because BZDs are **GABA-facilitatory**; they increase the *frequency* of chloride channel opening but require the presence of endogenous GABA to function. In contrast, barbiturates are GABA-mimetic (increase *duration* of opening) and can open channels directly at high doses, leading to fatal respiratory depression and coma. Therefore, BZD overdose is rarely fatal unless combined with other CNS depressants [1]. **Why other options are incorrect:** * **A. They alter sleep patterns more than other sedatives:** Incorrect. BZDs actually preserve sleep architecture better than barbiturates. While they do decrease REM sleep and Stage 4 NREM, the effect is less pronounced than with older sedatives. * **B. All benzodiazepines have pharmacologically active metabolites:** Incorrect. Several BZDs bypass phase I oxidative metabolism and are directly conjugated (Phase II) [2]. These are remembered by the mnemonic **LOT**: **L**orazepam, **O**xazepam, and **T**emazepam. They are preferred in elderly patients or those with liver failure [2]. * **C. They induce liver enzymes:** Incorrect. Unlike barbiturates, which are potent inducers of CYP450 enzymes (leading to numerous drug interactions), BZDs do not induce hepatic microsomal enzymes [1]. **High-Yield Clinical Pearls for NEET-PG:** * **Mechanism:** BZDs bind to the BZD-site on the $\text{GABA}_\text{A}$ receptor (between $\alpha$ and $\gamma$ subunits). * **Antidote:** **Flumazenil** is a specific BZD receptor antagonist used for overdose (Note: It can precipitate seizures in dependent patients) [3]. * **Shortest Acting BZD:** Midazolam (used for conscious sedation). * **Longest Acting BZD:** Flurazepam/Diazepam (due to active metabolites) [2].

Question 295: Vigabatrin acts by:

A. GABA-antagonism
B. GABA-agonism (Correct Answer)
C. NMDA-antagonism
D. Carbonic anhydrase activity

Explanation: **Vigabatrin** is a second-generation antiepileptic drug primarily used in the management of refractory focal seizures and infantile spasms. ### **Mechanism of Action** The correct answer is **GABA-agonism** (specifically, increasing GABAergic tone). Vigabatrin acts as a structural analogue of GABA and functions as an **irreversible inhibitor of GABA-transaminase (GABA-T)**. GABA-T is the enzyme responsible for the degradation of GABA in the synaptic cleft. By inhibiting this enzyme, Vigabatrin significantly increases the concentration of GABA (the primary inhibitory neurotransmitter) in the brain, thereby enhancing inhibitory neurotransmission and suppressing seizure activity. ### **Analysis of Incorrect Options** * **A. GABA-antagonism:** Antagonizing GABA (e.g., Picrotoxin or Bicuculline) would decrease inhibition, leading to CNS excitation and seizures, which is the opposite of the desired therapeutic effect. * **C. NMDA-antagonism:** This is the mechanism for drugs like Ketamine, Memantine, or Felbamate. While reducing glutamate-mediated excitation is an anticonvulsant strategy, it is not how Vigabatrin works. * **D. Carbonic anhydrase activity:** This refers to drugs like Acetazolamide, Topiramate, or Zonisamide, which cause mild systemic acidosis and alter CO2 levels in the brain to reduce excitability. ### **High-Yield Clinical Pearls for NEET-PG** * **Drug of Choice:** Vigabatrin is the first-line treatment for **Infantile Spasms (West Syndrome)** associated with **Tuberous Sclerosis**. * **Major Side Effect:** It is notorious for causing **permanent bilateral concentric visual field contraction** (Vigabatrin-induced visual field loss), necessitating regular perimetry monitoring. * **Mnemonic:** **Vi-GABA-Tr**ansaminase **In**hibitor (**Vi-GABA-Tr-In**).

Question 296: Which drug is used for the long-term treatment of partial seizures?

A. Valproate
B. Carbamazepine (Correct Answer)
C. Eptoin
D. Phenobarbitone

Explanation: **Explanation:** **Carbamazepine (CBZ)** is considered a first-line drug for the long-term management of **focal (partial) seizures**, including both simple and complex partial seizures, as well as focal seizures evolving into bilateral tonic-clonic seizures [1]. Its mechanism of action involves the blockade of voltage-gated sodium channels in their inactivated state, preventing high-frequency repetitive firing of neurons [2]. **Analysis of Options:** * **Carbamazepine (Correct):** It is highly effective for focal seizures and is often preferred over older agents due to a relatively better side-effect profile during long-term use [1]. * **Valproate:** While Valproate is a broad-spectrum anticonvulsant and *can* be used for focal seizures, it is the **drug of choice for generalized seizures** (especially Absence, Myoclonic, and Atonic seizures) [1]. * **Eptoin (Phenytoin):** Although effective for focal seizures, its non-linear (zero-order) kinetics and significant long term side effects (gum hyperplasia, hirsutism, osteomalacia) make it less ideal than Carbamazepine for primary long-term management [1]. * **Phenobarbitone:** This is a sedative-hypnotic used as a second-line agent. Due to side effects like cognitive impairment, hyperactivity in children, and sedation, it is rarely the first choice for long-term focal seizure therapy in modern practice. **NEET-PG High-Yield Pearls:** * **Drug of Choice (DOC):** Carbamazepine is the DOC for **Trigeminal Neuralgia** [1]. * **Side Effects:** Watch for **SIADH** (hyponatremia), Stevens-Johnson Syndrome (associated with HLA-B*1502), and diplopia. * **Metabolism:** It is a potent **enzyme inducer** and exhibits **auto-induction** (it induces its own metabolism). * **Contraindication:** Carbamazepine can **worsen** Absence and Myoclonic seizures.

Question 297: Which of the following is a melatonin receptor agonist?

A. Zolpidem
B. Ramelteon (Correct Answer)
C. Zolmitriptan
D. Zopiclone

Explanation: **Explanation:** **Correct Answer: B. Ramelteon** Ramelteon is a potent, selective agonist at **MT1 and MT2 receptors** located in the suprachiasmatic nucleus (SCN) of the hypothalamus. Unlike traditional sedatives, it mimics the action of endogenous melatonin to regulate the circadian rhythm and promote sleep onset. It is specifically indicated for sleep-onset insomnia and is unique because it lacks affinity for GABA receptors, meaning it has **no potential for abuse or dependence** (it is not a controlled substance). **Analysis of Incorrect Options:** * **A & D (Zolpidem and Zopiclone):** These are "Z-drugs" or non-benzodiazepine hypnotics. They act as agonists at the **GABA-A receptor** (specifically the α1 subunit). While they are used for insomnia, their mechanism is entirely different from melatonin agonists. * **C (Zolmitriptan):** This is a "Triptan" used in the acute treatment of migraine. It acts as a selective agonist at **5-HT 1B/1D receptors**, causing cranial vasoconstriction and inhibition of pro-inflammatory neuropeptide release. **High-Yield Clinical Pearls for NEET-PG:** * **Tasimelteon:** Another melatonin agonist specifically approved for "Non-24-hour sleep-wake disorder," commonly seen in totally blind individuals. * **Metabolism:** Ramelteon is primarily metabolized by **CYP1A2**. It should be avoided in patients taking Fluvoxamine (a potent CYP1A2 inhibitor). * **Side Effects:** Unlike benzodiazepines, Ramelteon does not cause rebound insomnia or withdrawal symptoms, but it may increase **prolactin levels** in some patients. * **Key Distinction:** Ramelteon helps with **sleep induction** (latency) but is less effective for sleep maintenance.

Question 298: Which of the following is NOT used in the early management of generalized convulsive status epilepticus?

A. Phenobarbitone (Correct Answer)
B. Phenytoin
C. Lorazepam
D. Valproate

Explanation: **Explanation:** The management of **Generalized Convulsive Status Epilepticus (GCSE)** follows a specific chronological protocol. The correct answer is **Phenobarbitone** because it is no longer considered a first-line or early-stage drug; it is reserved for refractory status epilepticus (Stage 3) after other agents have failed. **Why Phenobarbitone is the correct choice (NOT used early):** Phenobarbitone has a slow onset of action and carries a high risk of respiratory depression and hypotension, especially when combined with benzodiazepines. [3] Modern guidelines (like the AES protocol) prioritize faster-acting or safer alternatives. **Analysis of Incorrect Options (Used in early management):** * **Lorazepam (Option C):** This is the **drug of choice** for the "Initial Emergent Phase" (0–20 mins). [4] It has a rapid onset and a longer duration of action in the brain compared to Diazepam. * **Phenytoin/Fosphenytoin (Option B):** These are standard "Second-stage" (20–40 mins) medications used if seizures continue after benzodiazepines. [2] Fosphenytoin is often preferred due to less local irritation. * **Valproate (Option D):** Sodium Valproate is now a preferred second-line agent alongside Phenytoin and Levetiracetam due to its high efficacy and better hemodynamic stability. [1] **NEET-PG High-Yield Pearls:** 1. **Drug of Choice (Initial):** IV Lorazepam (0.1 mg/kg). [4] 2. **If IV access is unavailable:** Intramuscular (IM) Midazolam is the preferred alternative. 3. **Definition Change:** Status Epilepticus is now clinically defined as continuous seizure activity lasting **>5 minutes** (operational definition) rather than the traditional 30 minutes. 4. **Refractory Status:** Defined as failure of both a benzodiazepine and a second-line agent; managed with Midazolam infusions, Propofol, or Thiopentone/Phenobarbitone.

Question 299: Which of the following is the most efficacious triptan for rapid relief of acute migraine attack?

A. Sumatriptan
B. Almotriptan
C. Rizatriptan (Correct Answer)
D. Naratriptan

Explanation: **Explanation:** **Rizatriptan** is considered the most efficacious oral triptan for the rapid relief of acute migraine. The clinical superiority of Rizatriptan (10 mg) lies in its **pharmacokinetic profile**: it has a faster onset of action (Tmax of ~1 hour) and higher oral bioavailability compared to the prototype drug, Sumatriptan. Clinical trials consistently show that Rizatriptan achieves higher rates of "pain-free status" at 2 hours than most other oral triptans. **Analysis of Options:** * **Sumatriptan (Option A):** The first-generation triptan. While the subcutaneous route is the fastest overall, its **oral** form has low bioavailability (~15%) and a slower onset than Rizatriptan. * **Almotriptan (Option B):** It has better bioavailability than Sumatriptan and a better side-effect profile, but it does not surpass Rizatriptan in terms of speed or peak efficacy. * **Naratriptan (Option D):** Known for having a longer half-life and fewer side effects, but it has a **slow onset of action** and lower potency. It is typically used for migraines with a longer duration or to prevent recurrence, rather than rapid relief. **High-Yield NEET-PG Pearls:** * **Mechanism of Action:** Triptans are **5-HT$_{1B/1D}$ agonists**. They cause cranial vasoconstriction (1B) and inhibit the release of pro-inflammatory neuropeptides (CGRP, Substance P) from trigeminal nerve endings (1D). * **Fastest Route:** Subcutaneous Sumatriptan is the fastest overall delivery method. * **Longest Acting:** **Frovatriptan** has the longest half-life (~26 hours), followed by Naratriptan. * **Contraindications:** Due to vasoconstrictive effects, triptans are contraindicated in patients with Ischemic Heart Disease (IHD), Prinzmetal angina, and uncontrolled hypertension.

Question 300: Which one of the following statements about phenytoin is accurate?

A. Displaces sulfonamides from plasma proteins
B. Drug of choice in myoclonic seizures
C. Half-life is increased if used with phenobarbital
D. Toxicity may occur with only small increments in dose (Correct Answer)

Explanation: **Explanation:** The correct answer is **D**. Phenytoin follows **Zero-order kinetics (Non-linear kinetics)** at therapeutic or high concentrations [1]. This occurs because the hepatic microsomal enzymes (CYP2C9 and CYP2C19) responsible for its metabolism become saturated. Once saturation occurs, the rate of metabolism remains constant regardless of the drug concentration. Consequently, even a small increase in dose can lead to a disproportionately large increase in plasma levels, rapidly reaching toxic ranges. **Analysis of Incorrect Options:** * **A:** Phenytoin is highly bound to plasma albumin. It is **displaced by** drugs like sulfonamides, salicylates, and valproate [1], rather than displacing them. This displacement increases the free (active) fraction of phenytoin, potentially leading to toxicity [1]. * **B:** Phenytoin is the drug of choice for Tonic-Clonic Seizures (GTCS) and Focal seizures [4]. However, it is **contraindicated in myoclonic and absence seizures** [4], as it can paradoxically worsen them. Levetiracetam or Valproate are preferred for myoclonic seizures. * **C:** Phenobarbital is an **enzyme inducer**. When co-administered, it increases the metabolism of phenytoin, thereby **decreasing** its half-life and plasma concentration. **NEET-PG High-Yield Pearls:** * **Fosphenytoin:** A water-soluble prodrug of phenytoin used IV to avoid local complications like "Purple Glove Syndrome" [2], [3]. * **Teratogenicity:** Causes **Fetal Hydantoin Syndrome** (cleft lip/palate, digital hypoplasia). * **Side Effects Mnemonic (PHENYTOIN):** **P**-450 induction, **H**irsutism [3], **E**nlarged gums (Gingival hyperplasia) [3], **N**ystagmus (earliest sign of toxicity), **Y**ellow-brown skin, **T**eratogenicity, **O**steomalacia [3], **I**nterference with B12/Folate (Megaloblastic anemia) [3], **N**europathy.

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