Central Nervous System Pharmacology Practice Questions

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.

Q: Levodopa can aggravate which of the following malignancies?

Malignant melanoma. **Explanation:** **Correct Answer: D. Malignant Melanoma** The correct answer is **Malignant Melanoma**. This association is based on the biochemical pathway shared by dopamine and melanin. Both substances are synthesized from the common precursor amino acid, **L-Tyrosine**. L-Tyrosine is converted to **L-Dopa** by the enzyme tyrosine hydroxylase. In the brain, L-Dopa is converted to dopamine; however, in melanocytes, L-Dopa is a crucial intermediate in the synthesis of melanin. It is hypothesized that exogenous administration of Levodopa may stimulate the activity of melanocytes or provide the substrate necessary for the rapid proliferation of malignant melanocytic cells. Consequently, Levodopa is strictly contraindicated in patients with a history of undiagnosed skin lesions or a known history of melanoma. **Analysis of Incorrect Options:** * **A, B, and C:** Squamous cell cancer, Pleomorphic adenoma, and Basal cell carcinoma do not involve the melanocytic pathway or the metabolic intermediates of catecholamine synthesis. There is no clinical or pharmacological evidence suggesting that Levodopa influences the progression of these specific tumors. **High-Yield Clinical Pearls for NEET-PG:** * **Pre-treatment screening:** Always perform a thorough skin examination before initiating Levodopa therapy in elderly patients. * **Vitamin B6 (Pyridoxine) Interaction:** Pyridoxine enhances the peripheral decarboxylation of Levodopa, reducing its availability to the CNS (unless given with Carbidopa). * **Dietary Interaction:** High-protein meals interfere with Levodopa absorption due to competition with aromatic amino acids for transport across the blood-brain barrier. * **Psychiatric Side Effects:** Levodopa can trigger visual hallucinations and psychosis due to increased dopaminergic activity in the mesolimbic pathway.

Q: Which of the following drugs has teratogenic potential?

Carbamazepine. **Explanation:** **Carbamazepine (Option A)** is the correct answer because it is a well-documented teratogen. It is associated with a 1% risk of **Neural Tube Defects (NTDs)**, specifically spina bifida, due to its interference with folate metabolism. Additionally, it can cause "Fetal Carbamazepine Syndrome," characterized by craniofacial defects, fingernail hypoplasia, and developmental delays. **Analysis of Incorrect Options:** * **Clonazepam (Option B):** While benzodiazepines were historically linked to cleft lip/palate, recent large-scale studies show that the absolute risk is very low. They are generally considered safer than older anticonvulsants like Valproate or Carbamazepine. * **Risperidone & Olanzapine (Options C & D):** These are atypical antipsychotics. Current evidence suggests they do not significantly increase the risk of major congenital malformations, though they may be associated with neonatal withdrawal symptoms or metabolic issues if used late in pregnancy. **High-Yield Clinical Pearls for NEET-PG:** 1. **Valproate** is the most teratogenic antiepileptic, causing the highest incidence of NTDs (up to 2–5%). 2. **Phenytoin** causes **Fetal Hydantoin Syndrome** (cleft lip/palate, microcephaly, and digital hypoplasia). 3. **Drug of Choice:** For a pregnant woman with epilepsy, **Levetiracetam** or **Lamotrigine** are preferred due to their superior safety profiles. 4. **Prevention:** All women on enzyme-inducing AEDs (like Carbamazepine) should receive **high-dose Folic Acid (5 mg/day)** pre-conceptionally to reduce NTD risk.

Question 1

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

Accepted Answer

Benzocaine

Answer

Procaine

Answer

Bupivacaine

Answer

Etidocaine

Question 2

What is the overall action of caffeine on heart rate?

Accepted Answer

Decreases

Answer

Increases

Answer

No effect

Answer

First increases then decreases

Question 3

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 4

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 5

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

Accepted Answer

Biperiden

Answer

Levodopa

Answer

Benserazide

Answer

Selegiline

Question 6

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 7

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

Question 8

Which of the following drugs can prevent or delay the onset of Alzheimer's disease?

Accepted Answer

NSAID

Answer

Tacrine

Answer

Donepezil

Answer

None of the above

Question 9

Levodopa can aggravate which of the following malignancies?

Accepted Answer

Malignant melanoma

Answer

Squamous cell cancer

Answer

Pleomorphic adenoma

Answer

Basal cell carcinoma

Question 10

Which of the following drugs has teratogenic potential?

Accepted Answer

Carbamazepine

Answer

Clonazepam

Answer

Risperidone

Answer

Olanzapine

Central Nervous System Pharmacology — MCQs

Central Nervous System Pharmacology — MCQs

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