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: 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 of the following anti-Parkinson drugs acts by decreasing brain cholinergic activity?

Biperiden. **Explanation:** **Underlying Concept:** Parkinson’s disease is characterized by a neurochemical imbalance in the basal ganglia: a **deficiency of Dopamine** (inhibitory) and a relative **excess of Acetylcholine** (excitatory). To restore balance, treatment strategies either increase dopaminergic tone or decrease cholinergic activity. **Why Biperiden is Correct:** **Biperiden** is a **centrally acting anticholinergic** drug. It works by blocking muscarinic receptors in the striatum, thereby decreasing the relative cholinergic overactivity. These drugs are particularly useful for treating tremors and managing drug-induced parkinsonism (extrapyramidal symptoms). **Analysis of Incorrect Options:** * **Levodopa (A):** A precursor of dopamine. It acts by increasing dopamine levels in the brain, not by decreasing acetylcholine. * **Benserazide (B):** A peripheral dopa-decarboxylase inhibitor. It does not cross the blood-brain barrier; its role is to prevent the peripheral metabolism of Levodopa, increasing its central bioavailability. * **Selegiline (C):** A selective MAO-B inhibitor. It acts by inhibiting the breakdown of dopamine in the CNS, thus prolonging dopaminergic action. **NEET-PG High-Yield Pearls:** * **Drug of Choice (DOC):** For drug-induced parkinsonism (caused by antipsychotics), centrally acting anticholinergics like **Biperiden** or **Trihexyphenidyl (Benzhexol)** are the drugs of choice. * **Contraindication:** Anticholinergics should be avoided in elderly patients due to the risk of confusion, urinary retention, and glaucoma. * **Benztropine** is another common central anticholinergic used in this category.

Q: Which of the following is true about benzodiazepines?

Lorazepam has a shorter duration of action than temazepam. ### Explanation **1. Why Option C is Correct:** Benzodiazepines (BZDs) are classified based on their duration of action, which is determined by their metabolism and the presence of active metabolites. **Lorazepam** is an intermediate-acting BZD with a half-life of 10–20 hours and **no active metabolites**. In contrast, **Temazepam**, while also intermediate-acting, typically exhibits a longer clinical duration of action in the context of sedative effects compared to Lorazepam. More importantly, Lorazepam is preferred in patients with liver dysfunction (along with Oxazepam and Temazepam—the "LOT" group) because it undergoes direct conjugation without phase I oxidative metabolism, leading to a predictable, shorter clearance profile. **2. Why Other Options are Incorrect:** * **Options A & B:** Benzodiazepines do not increase or antagonize the *release* of GABA. Instead, they act as **positive allosteric modulators**. They bind to the BZD site on the $GABA_A$ receptor, increasing the **frequency** of chloride channel opening in the presence of GABA. * **Option D:** **Flumazenil** is the specific competitive antagonist for benzodiazepines. Atropine is a muscarinic antagonist used for organophosphate poisoning or bradycardia. **3. High-Yield NEET-PG Pearls:** * **Mechanism of Action:** BZDs increase the **frequency** of $Cl^-$ channel opening; Barbiturates increase the **duration**. * **Metabolism (LOT):** **L**orazepam, **O**xazepam, and **T**emazepam are metabolized via glucuronidation (Phase II) only. They are safe in the elderly and those with liver failure. * **Drug of Choice:** * Status Epilepticus: **Lorazepam** (IV). * Alcohol Withdrawal: **Chlordiazepoxide** (or Lorazepam if liver is damaged). * Panic Disorder: **Alprazolam**. * **Antidote:** Flumazenil can precipitate seizures in BZD-dependent patients or in mixed TCA overdoses.

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

Why is the effect of local anesthesia slow in infected tissues?

Accepted Answer

Low extracellular pH that hinders diffusion of the drug into the cell.

Answer

Less vascularity causing poor diffusion of drug.

Answer

Rich in enzymes that metabolize the drug.

Answer

Rich in K+ that inhibits the binding of the drug to the receptor.

Question 3

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

Accepted Answer

Phenytoin

Answer

Carbamazepine

Answer

Sodium valproate

Answer

Phenobarbital

Question 4

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

Accepted Answer

Benzocaine

Answer

Procaine

Answer

Bupivacaine

Answer

Etidocaine

Question 5

What is the overall action of caffeine on heart rate?

Accepted Answer

Decreases

Answer

Increases

Answer

No effect

Answer

First increases then decreases

Question 6

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 7

Which of the following statements about anti-epileptics is false?

Accepted Answer

Lamotrigine mainly acts by causing GABA mediated Cl- channel opening.

Answer

Phenytoin and carbamazepine act by prolonging the inactivated state of Na+ channels.

Answer

Carbamazepine can be used in trigeminal neuralgias.

Answer

Diazepam is an anticonvulsant drug.

Question 8

Which of the following anti-Parkinson drugs acts by decreasing brain cholinergic activity?

Accepted Answer

Biperiden

Answer

Levodopa

Answer

Benserazide

Answer

Selegiline

Question 9

Hallucinations, psychosis, hypertension, and tachycardia are adverse effects typically associated with which of the following narcotics?

Accepted Answer

Pentazocine

Answer

Morphine

Answer

Meperidine

Answer

Buprenorphine

Question 10

Which of the following is true about benzodiazepines?

Accepted Answer

Lorazepam has a shorter duration of action than temazepam

Answer

Increased release of GABA

Answer

Antagonizing release of GABA

Answer

Atropine is its antagonist

Central Nervous System Pharmacology — MCQs

Central Nervous System Pharmacology — MCQs

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