Central Nervous System Pharmacology Practice Questions

Q: Pseudolymphoma can result from long-term use of which medication?

Phenytoin. **Explanation:** **Phenytoin** is a well-known cause of **Pseudolymphoma** (also known as Phenytoin-induced lymphadenopathy). This is a hypersensitivity reaction characterized by fever, skin rash, and generalized lymphadenopathy that clinically and histologically mimics Hodgkin’s or non-Hodgkin’s lymphoma. The condition is usually benign and reversible upon discontinuation of the drug, though in rare cases, it may progress to true malignant lymphoma. **Analysis of Options:** * **Phenytoin (Correct):** It induces a type IV hypersensitivity reaction. It is also associated with "DRESS syndrome" (Drug Reaction with Eosinophilia and Systemic Symptoms). * **Carbamazepine:** While it can cause skin rashes (Stevens-Johnson Syndrome) and blood dyscrasias (aplastic anemia), it is not classically associated with pseudolymphoma. * **Sodium Valproate:** Common side effects include weight gain, hepatotoxicity, alopecia, and pancreatitis, but not lymphadenopathy. * **Phenobarbital:** Primarily causes sedation, cognitive impairment, and osteomalacia; it does not typically cause pseudolymphoma. **High-Yield Clinical Pearls for NEET-PG:** * **Mnemonic for Phenytoin Side Effects (PH_E_NYTOIN):** **P**-P450 inducer, **H**-Hirsutism, **E**-Enlarged gums (Gingival hyperplasia), **N**-Nystagmus, **Y**-Yellow-brown skin (Pigmentation), **T**-Teratogenicity (Fetal Hydantoin Syndrome), **O**-Osteomalacia, **I**-Interference with B12/Folate (Megaloblastic anemia), **N**-Neuropathy & **N**-Nodes (Pseudolymphoma). * **Gingival Hyperplasia:** Caused by increased expression of Platelet-Derived Growth Factor (PDGF). * **Zero-order Kinetics:** Phenytoin follows saturation kinetics at therapeutic doses.

Q: Concomitant administration of clonazepam with which of the following antiepileptic drugs can precipitate absence status?

Sodium valproate. **Explanation:** The correct answer is **Sodium Valproate**. **Mechanism of Interaction:** The precipitation of **absence status (non-convulsive status epilepticus)** is a well-documented, though rare, idiosyncratic drug interaction between **clonazepam** and **sodium valproate**. While both drugs are individually effective in treating absence seizures, their concomitant use can paradoxically trigger prolonged absence attacks. The exact pathophysiology is not fully understood, but it is hypothesized to involve complex alterations in GABAergic neurotransmission within the thalamocortical pathways, which are responsible for the 3-Hz spike-and-wave discharges characteristic of absence epilepsy. **Analysis of Incorrect Options:** * **Phenobarbitone:** This is a barbiturate that increases the duration of GABA-A channel opening. While it causes sedation when used with benzodiazepines, it does not specifically precipitate absence status. * **Carbamazepine & Phenytoin:** These are sodium channel blockers. They are generally **contraindicated** in absence seizures because they can aggravate them, but they do not have a specific "status-precipitating" interaction with clonazepam. **High-Yield Clinical Pearls for NEET-PG:** * **Drug of Choice (DOC):** Sodium Valproate is the DOC for generalized tonic-clonic seizures (GTCS) and myoclonic seizures. Ethosuximide is the DOC for pure absence seizures. * **Paradoxical Effect:** Always remember the "Valproate + Clonazepam = Absence Status" triad for pharmacology MCQs. * **Contraindication:** Avoid Carbamazepine, Phenytoin, and Vigabatrin in patients with absence or myoclonic seizures as they can worsen the condition. * **Valproate Side Effects:** Hepatotoxicity (highest risk <2 years old), Teratogenicity (Neural tube defects), and Weight gain.

Q: Which of the following antiepileptic agents does not act by Na+ channel modulation?

Vigabatrin. **Explanation:** The mechanism of action of antiepileptic drugs (AEDs) is a high-yield topic for NEET-PG. To answer this, one must distinguish between drugs that stabilize membranes via ion channels and those that enhance inhibitory neurotransmission. **1. Why Vigabatrin is the Correct Answer:** Vigabatrin does **not** act on sodium channels. Its mechanism is the **irreversible inhibition of GABA transaminase (GABA-T)**, the enzyme responsible for the degradation of GABA. By blocking this enzyme, Vigabatrin increases the concentration of GABA (the primary inhibitory neurotransmitter) in the synaptic cleft. **2. Analysis of Incorrect Options (Na+ Channel Blockers):** * **Phenytoin:** A classic sodium channel blocker that shows use-dependent (voltage-dependent) blockade, prolonging the inactivated state of the channel. * **Valproate:** A broad-spectrum AED with multiple mechanisms, but its primary action includes the blockade of voltage-gated sodium channels and T-type calcium channels. * **Lamotrigine:** Primarily acts by blocking voltage-gated sodium channels, which subsequently inhibits the release of excitatory neurotransmitters like glutamate. **Clinical Pearls for NEET-PG:** * **Vigabatrin Side Effect:** Associated with **permanent bilateral concentric visual field defects** (requires regular perimetry). * **Drug of Choice:** Vigabatrin is the drug of choice for **Infantile Spasms** associated with **Tuberous Sclerosis**. * **Other GABA-acting drugs:** Tiagabine (GAT-1 inhibitor), Diazepam/Phenobarbitone (GABA-A receptor modulators). * **Mnemonic for Na+ blockers:** "The **L**ame **P**heny **V**alue **C**ard" (**L**amotrigine, **P**henytoin, **V**alproate, **C**arbamazepine).

Q: Which of the following local anesthetics is useful for topical administration only?

Benzocaine. **Explanation:** The correct answer is **Benzocaine**. Local anesthetics (LAs) are categorized based on their solubility and clinical utility. **Benzocaine** is a PABA derivative characterized by very low water solubility. Due to this property, it is absorbed too slowly to be effective or safe for injection (as it could cause local tissue irritation or remain at the site indefinitely). However, its poor solubility makes it ideal for **topical/surface anesthesia**, as it stays on the mucous membranes or skin for a prolonged duration without significant systemic absorption. **Analysis of Incorrect Options:** * **Procaine (Option A):** An ester-type LA with low lipid solubility and potency. It is primarily used for infiltration and spinal anesthesia but has **poor topical activity** because it does not penetrate mucous membranes effectively. * **Bupivacaine (Option B):** A potent, long-acting amide LA used extensively for infiltration, nerve blocks, and spinal/epidural anesthesia. It is not used as a standalone topical agent. * **Etidocaine (Option C):** A long-acting amide LA similar to lidocaine but with a more profound motor block. It is used for regional nerve blocks and infiltration, not exclusively for topical use. **High-Yield Clinical Pearls for NEET-PG:** * **Methemoglobinemia:** Benzocaine is a classic trigger for methemoglobinemia (treated with Methylene Blue). * **Classification:** LAs are divided into **Esters** (Procaine, Benzocaine, Tetracaine, Cocaine) and **Amides** (Lidocaine, Bupivacaine, Ropivacaine). *Mnemonic: Amides have two "i"s in their name.* * **Cocaine:** The only LA that is a naturally occurring alkaloid and possesses intrinsic vasoconstrictor properties. * **Lidocaine:** The most versatile LA, used for both topical and injectable routes, and also as a Class IB antiarrhythmic.

Q: Baclofen acts as which of the following?

GABAB receptor agonist. **Explanation:** **Baclofen** is a centrally acting skeletal muscle relaxant primarily used to treat spasticity. Its mechanism of action is rooted in its role as a selective **GABA$_B$ receptor agonist**. 1. **Why Option B is Correct:** GABA$_B$ receptors are G-protein coupled receptors (metabotropic) located both pre-synaptically and post-synaptically in the spinal cord. Baclofen mimics the inhibitory effects of GABA at these sites. By activating these receptors, it increases potassium ($K^+$) conductance (hyperpolarization) and inhibits calcium ($Ca^{2+}$) influx. This results in the inhibition of both monosynaptic and polysynaptic reflexes in the spinal cord, leading to reduced muscle spasticity. 2. **Why Other Options are Incorrect:** * **Options A & C:** GABA$_A$ receptors are ionotropic (ligand-gated chloride channels). Drugs like Benzodiazepines and Barbiturates modulate GABA$_A$ receptors, not Baclofen. * **Option D:** A GABA$_B$ antagonist (e.g., Saclofen) would block inhibitory signals, potentially increasing neuronal excitability, which is the opposite of Baclofen’s therapeutic goal. **Clinical Pearls for NEET-PG:** * **Clinical Use:** It is the drug of choice for spasticity resulting from **Multiple Sclerosis** and spinal cord injuries. * **Route:** Can be administered orally or via an **intrathecal pump** for severe cases. * **Side Effects:** Drowsiness, fatigue, and muscle weakness. * **Withdrawal Warning:** Sudden discontinuation of Baclofen can lead to visual hallucinations, tachycardia, and seizures; it must be tapered gradually. * **Comparison:** Unlike Diazepam (which acts on GABA$_A$), Baclofen causes less sedation at therapeutic doses.

Q: Which non-synthetic alkaloid compound acts similarly to amphetamine?

All of the above. **Explanation:** The correct answer is **D. All of the above**. The underlying medical concept is that **Amphetamine** is a potent CNS stimulant that acts as an indirect sympathomimetic by increasing the synaptic concentration of monoamines (Dopamine, Norepinephrine, and Serotonin). While amphetamine itself is a synthetic compound, several **non-synthetic alkaloids** (naturally occurring nitrogenous organic compounds) mimic its stimulatory effects through various mechanisms: * **Cocaine:** A natural alkaloid derived from *Erythroxylum coca*. Like amphetamine, it increases synaptic monoamines, specifically by **blocking the reuptake** of Dopamine, Norepinephrine, and Serotonin (DAT, NET, and SERT inhibitors). * **Caffeine:** A methylxanthine alkaloid found in coffee beans and tea leaves. It acts as an **adenosine receptor antagonist**. Since adenosine normally inhibits the release of excitatory neurotransmitters, caffeine results in increased CNS activity, mimicking the alertness produced by amphetamine. * **Nicotine:** A pyrrolidine alkaloid found in *Nicotiana tabacum*. It stimulates **nicotinic acetylcholine receptors (nAChRs)**, leading to the downstream release of dopamine and adrenaline, producing stimulant effects similar to low-dose amphetamines. **High-Yield Clinical Pearls for NEET-PG:** * **Mechanism Distinction:** Amphetamine *releases* stored catecholamines (via VMAT-2 and TAAR1), whereas Cocaine *blocks reuptake*. * **Ephedrine & Cathinone:** These are other important naturally occurring alkaloids (from *Ephedra* and *Khat*) that are structurally and functionally similar to amphetamine. * **Toxicity:** Overdose of any of these stimulants typically presents with a **Sympathomimetic Toxidrome** (tachycardia, hypertension, mydriasis, and diaphoresis). Note: Cocaine is unique as it also possesses local anesthetic properties (sodium channel blockade).

Question 1

Sumatriptan is contraindicated in which of the following conditions?

Accepted Answer

Peripheral vascular disease

Answer

Asthma

Answer

Diabetes Mellitus (DM)

Answer

Sepsis

Question 2

Pseudolymphoma can result from long-term use of which medication?

Accepted Answer

Phenytoin

Answer

Carbamazepine

Answer

Sodium valproate

Answer

Phenobarbital

Question 3

Concomitant administration of clonazepam with which of the following antiepileptic drugs can precipitate absence status?

Accepted Answer

Sodium valproate

Answer

Phenobarbitone

Answer

Carbamazepine

Answer

Phenytoin

Question 4

Which of the following antiepileptic agents does not act by Na+ channel modulation?

Accepted Answer

Vigabatrin

Answer

Phenytoin

Answer

Valproate

Answer

Lamotrigine

Question 5

Which of the following drug classes, if combined with Rivastigmine, decreases its efficacy?

Accepted Answer

Tricyclic antidepressants

Answer

Selective serotonin reuptake inhibitors

Answer

Reversible inhibitor of MAO-A

Answer

Atypical antidepressants

Question 6

Which of the following local anesthetics is useful for topical administration only?

Accepted Answer

Benzocaine

Answer

Procaine

Answer

Bupivacaine

Answer

Etidocaine

Question 7

Regarding opioid-induced seizures, which statement is correct?

Accepted Answer

Children are more susceptible.

Answer

They usually occur at therapeutic doses.

Answer

Seizures occur only with 0-opioid agonists.

Answer

Diazepam is the drug of choice in treatment.

Question 8

Which of the following calcium channel blockers is indicated for increased intracranial tension?

Accepted Answer

Nimodipine

Answer

Nicardipine

Answer

Clevidipine

Answer

Nitrendipine

Question 9

Baclofen acts as which of the following?

Accepted Answer

GABAB receptor agonist

Answer

GABAA receptor agonist

Answer

GABAA receptor antagonist

Answer

GABAB receptor antagonist

Question 10

Which non-synthetic alkaloid compound acts similarly to amphetamine?

Accepted Answer

All of the above

Answer

Caffeine

Answer

Cocaine

Answer

Nicotine

Central Nervous System Pharmacology — MCQs

Central Nervous System Pharmacology — MCQs

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