Central Nervous System Pharmacology Practice Questions

Q: Amide type of local anesthetic agents undergo biotransformation primarily in which organ?

Liver. **Explanation:** Local anesthetics (LAs) are chemically classified into two categories based on their intermediate chain: **Amides** and **Esters**. The site of metabolism is the fundamental difference between these two groups. **1. Why Liver is Correct:** Amide-type local anesthetics (e.g., Lidocaine, Bupivacaine, Ropivacaine) undergo complex biotransformation primarily in the **liver** via **microsomal P450 enzymes** (specifically N-dealkylation and hydroxylation). Because their clearance depends on hepatic blood flow and enzyme function, patients with liver failure or congestive heart failure are at a higher risk of systemic toxicity (LAST). **2. Why other options are incorrect:** * **Plasma:** This is the primary site for **Ester-type** local anesthetics (e.g., Procaine, Tetracaine, Benzocaine). They are rapidly hydrolyzed by **pseudocholinesterase** (plasma cholinesterase). * **Kidney:** While the kidneys are the primary route for **excretion** of the metabolites, they are not the primary site of metabolism. * **Excreted in unaltered form:** Only a very small fraction (<5%) of local anesthetics is excreted unchanged in the urine. **High-Yield Clinical Pearls for NEET-PG:** * **Mnemonic:** Amides have two "i"s in their name (L**i**doca**i**ne, Pr**i**loca**i**ne, Bup**i**vaca**i**ne), while Esters have only one (Proca**i**ne, Chloroproca**i**ne). * **Prilocaine Metabolism:** A metabolite of prilocaine (o-toluidine) can cause **methemoglobinemia**, treated with Methylene Blue. * **Rate of Metabolism:** Esters are metabolized much faster than amides, making esters generally less likely to cause systemic toxicity but more likely to cause allergic reactions (due to PABA formation).

Q: Which ester local anesthetic undergoes significant liver metabolism?

Cocaine. **Explanation:** Local anesthetics (LAs) are classified into two groups based on their chemical linkage: **Esters** and **Amides**. The primary metabolic pathway for most ester LAs is rapid hydrolysis by **pseudocholinesterase** (plasma cholinesterase) in the blood. **Why Cocaine is the Correct Answer:** Cocaine is a unique ester local anesthetic. Unlike other esters that are metabolized almost exclusively in the plasma, **Cocaine undergoes significant metabolism in the liver** via carboxylesterase enzymes. While some of it is hydrolyzed by plasma cholinesterase, the hepatic pathway is a major route for its transformation into metabolites like benzoylecgonine (which is excreted in the urine). **Analysis of Incorrect Options:** * **Procaine & Chloroprocaine:** These are classic esters with very short half-lives. They are rapidly and completely hydrolyzed by plasma pseudocholinesterase. Chloroprocaine is the shortest-acting LA due to this rapid metabolism. * **Tetracaine:** A long-acting ester, it is also metabolized by plasma pseudocholinesterase, though at a slower rate than procaine. **NEET-PG High-Yield Pearls:** 1. **Metabolism Rule:** Remember the "i" rule. Am**i**des (Lidocaine, Bupivacaine, Ropivacaine) have two "i"s in their name and are metabolized in the **Liver**. Esters (one "i") are metabolized in the **Plasma**. Cocaine is the notable exception. 2. **Vasoconstriction:** Cocaine is the only local anesthetic that causes **vasoconstriction** by blocking the reuptake of norepinephrine. All other LAs (except to some extent Ropivacaine/Levobupivacaine) are vasodilators. 3. **PABA:** Metabolism of ester LAs produces **para-aminobenzoic acid (PABA)**, which is responsible for the higher incidence of allergic reactions compared to amides.

Q: Which of the following statements is true regarding carbamazepine?

Used in the treatment of trigeminal neuralgia.. **Explanation:** **Carbamazepine** is a sodium channel blocker that stabilizes hyperexcitable nerve membranes. 1. **Why Option A is Correct:** Carbamazepine is the **drug of choice (DOC) for Trigeminal Neuralgia**. It works by reducing the frequency of paroxysmal discharges in the trigeminal nerve, providing significant pain relief for this specific neuropathic condition. 2. **Analysis of Incorrect Options:** * **Option B:** While Carbamazepine is indeed a potent **enzyme inducer** (inducing CYP3A4 and its own metabolism—autoinduction), the question asks for the "true statement" in a context where Option A is the most clinically definitive primary indication. *Note: In many competitive exams, if multiple statements are technically true, the one defining the drug's primary clinical utility is prioritized.* * **Option C:** Carbamazepine is associated with **aplastic anemia** and agranulocytosis, not megaloblastic anemia. Megaloblastic anemia is a classic side effect of **Phenytoin** (due to folate interference). * **Option D:** The drug of choice for **Status Epilepticus** is intravenous **Lorazepam** (or Diazepam), followed by Fosphenytoin/Phenytoin. Carbamazepine is contraindicated in absence and myoclonic seizures as it may worsen them. **High-Yield Clinical Pearls for NEET-PG:** * **Mechanism:** Blocks voltage-gated $Na^+$ channels in the inactivated state. * **DOC for:** Trigeminal neuralgia and Partial (Focal) seizures. * **Side Effects:** Diplopia, Ataxia, **SIADH** (Hyponatremia), and potentially fatal skin reactions like **Stevens-Johnson Syndrome** (associated with the HLA-B*1502 allele). * **Teratogenicity:** Can cause neural tube defects (Spina Bifida).

Q: D2 receptors are maximally seen in which area?

Corpus striatum. **Explanation:** The correct answer is **Corpus striatum**. Dopamine D2 receptors are G-protein coupled receptors (Gi/o) that inhibit adenylyl cyclase. In the brain, they are most densely concentrated in the **Corpus striatum** (comprising the caudate nucleus and putamen). This area is the primary hub of the **Nigrostriatal pathway**, where dopamine is released from the substantia nigra pars compacta to modulate motor control. **Analysis of Options:** * **Corpus striatum (Correct):** It contains the highest density of D2 receptors. This is clinically significant because the blockade of these receptors by antipsychotics (especially first-generation) leads to Extrapyramidal Side Effects (EPS). * **Nucleus accumbens:** While this area is rich in D2 receptors, it is part of the **Mesolimbic pathway** (involved in reward and addiction). The density here is high but remains secondary to the corpus striatum. * **Frontal lobe:** This area is primarily associated with the **Mesocortical pathway**. It contains a higher ratio of D1 and D4 receptors compared to D2. * **Cerebellum:** This region has a very low density of dopamine receptors, as its primary neurotransmitters are GABA and Glutamate. **Clinical Pearls for NEET-PG:** 1. **D2 Blockade:** Antipsychotic potency is directly correlated with their binding affinity for D2 receptors. 2. **Nigrostriatal Pathway:** Blockade here causes EPS (Parkinsonism, Akathisia, Dystonia). 3. **Mesolimbic Pathway:** Blockade here treats the "positive symptoms" of Schizophrenia. 4. **Tuberoinfundibular Pathway:** D2 blockade here leads to hyperprolactinemia (Dopamine is the Prolactin Inhibiting Factor).

Q: Levodopa is contraindicated in which of the following conditions?

Angle closure glaucoma. **Explanation:** **Why Angle Closure Glaucoma is the Correct Answer:** Levodopa is a precursor of dopamine, which is further metabolized into norepinephrine and epinephrine. These catecholamines act on **$\alpha_1$-adrenergic receptors**, causing mydriasis (dilation of the pupil). In patients with a narrow iridocorneal angle, mydriasis can further obstruct the outflow of aqueous humor, leading to a dangerous and acute rise in intraocular pressure (IOP). Therefore, it is strictly contraindicated in **angle-closure (narrow-angle) glaucoma**. However, it can be used cautiously in chronic open-angle glaucoma if IOP is well-controlled. **Analysis of Incorrect Options:** * **A. Hypertension:** While Levodopa can cause transient cardiac arrhythmias or orthostatic hypotension, it is not an absolute contraindication. Blood pressure should be monitored, but it is not a primary contraindication like narrow-angle glaucoma. * **B. Multiple Sclerosis:** This is a demyelinating disease of the CNS. Levodopa has no significant interaction with the pathophysiology of MS and is neither indicated nor contraindicated. * **C. Pheochromocytoma:** While catecholamine-producing tumors require caution with drugs affecting dopamine/norepinephrine, the most definitive and high-yield contraindication among the choices provided for NEET-PG is angle-closure glaucoma. **Clinical Pearls for NEET-PG:** * **Absolute Contraindications of Levodopa:** Angle-closure glaucoma, undiagnosed skin lesions (may activate **malignant melanoma**), and use of **Non-selective MAO inhibitors** (risk of hypertensive crisis). * **Vitamin Interaction:** Pyridoxine (Vitamin B6) increases the peripheral decarboxylation of Levodopa, reducing its CNS availability (unless given with Carbidopa). * **Side Effects:** The "On-Off" phenomenon and dyskinesias are common long-term complications.

Q: Which of the following can be used in the treatment of myoclonic seizures, except?

Carbamazepine. **Explanation:** The correct answer is **Carbamazepine**. **1. Why Carbamazepine is the correct answer:** In the treatment of **Myoclonic seizures**, certain sodium channel blockers like **Carbamazepine**, **Phenytoin**, and **Oxcarbazepine** are strictly contraindicated. These drugs can paradoxically **exacerbate** or worsen myoclonic and absence seizures. The underlying mechanism involves the enhancement of GABA-mediated inhibitory currents in the thalamocortical circuit or the specific blockade of sodium channels that may inadvertently increase the synchrony of neuronal firing in these specific seizure types. **2. Why the other options are incorrect:** * **Valproate (Option A):** This is the **drug of choice** for myoclonic seizures. It has a broad spectrum of activity, affecting sodium channels, T-type calcium channels, and increasing GABA levels. * **Topiramate (Option C):** A broad-spectrum anti-epileptic drug (AED) that is effective against multiple seizure types, including myoclonic seizures, due to its multiple mechanisms (Na+ channel blockade, AMPA/Kainate antagonism, and GABA enhancement). * **Zonisamide (Option D):** Another broad-spectrum agent that is effective in treating myoclonic jerks, particularly in progressive myoclonic epilepsies. **3. High-Yield Clinical Pearls for NEET-PG:** * **Broad-spectrum AEDs** (Valproate, Levetiracetam, Topiramate, Zonisamide, Lamotrigine) are generally safe for myoclonic seizures. * **Narrow-spectrum AEDs** (Carbamazepine, Phenytoin, Gabapentin, Pregabalin, Vigabatrin) should be **avoided** in myoclonic and absence seizures as they can worsen the condition. * **Drug of Choice (DOC) Summary:** * Myoclonic Seizures: **Valproate** * Absence Seizures: **Ethosuximide** (Valproate if generalized tonic-clonic seizures are also present). * Trigeminal Neuralgia: **Carbamazepine**.

Q: Valproic acid causes all EXCEPT-

It is an enzyme inducer. **Explanation:** The correct answer is **A (It is an enzyme inducer)** because Valproic acid is actually a potent **microsomal enzyme inhibitor**. Unlike most older antiepileptics (like Phenytoin, Carbamazepine, and Phenobarbitone) which induce CYP450 enzymes, Valproic acid inhibits them. This leads to significant drug interactions, such as increasing the plasma levels of Phenobarbital and Lamotrigine when co-administered. **Analysis of other options:** * **B (Obesity):** Weight gain is a very common side effect of Valproate therapy, often leading to metabolic issues and decreased compliance. * **C (Hirsutism):** This is a tricky point in pharmacology. While Valproate is classically associated with **alopecia** (hair loss/thinning), it is also a key cause of **Polycystic Ovarian Syndrome (PCOS)** in female patients. PCOS presents with hormonal imbalances that lead to **hirsutism** and acne. * **D (Neural tube defects):** Valproate is highly teratogenic. It interferes with folate metabolism, specifically increasing the risk of **Spina Bifida** (neural tube defects) if taken during pregnancy. **High-Yield Clinical Pearls for NEET-PG:** * **Mnemonic for Valproate Side Effects (VALPROATE):** **V**omiting, **A**lopecia, **L**iver toxicity (Hepatotoxicity), **P**ancreatitis/PCOS, **R**etention of fat (Obesity), **O**edema, **A**norexia, **T**eratogenicity, **E**nzyme inhibitor. * **Drug of Choice:** Valproate is the drug of choice for **Myoclonic seizures** and is a broad-spectrum agent used for Generalized Tonic-Clonic Seizures (GTCS) and Absence seizures. * **Hepatotoxicity:** It is contraindicated in children under 2 years due to the risk of fatal fulminant hepatitis.

Q: What is the primary classification of Baclofen?

Centrally acting muscle relaxant. **Explanation:** **Baclofen** is a structural analog of the inhibitory neurotransmitter Gamma-Aminobutyric Acid (GABA). It is classified as a **centrally acting muscle relaxant** because its primary site of action is within the spinal cord. **Mechanism of Action:** Baclofen acts as a selective **GABA-B receptor agonist**. By stimulating these receptors in the dorsal horn of the spinal cord, it induces hyperpolarization. This leads to: 1. **Presynaptic inhibition:** Reducing the release of excitatory neurotransmitters (like glutamate and aspartate). 2. **Postsynaptic inhibition:** Reducing the excitability of alpha motor neurons. The result is a reduction in the frequency and severity of muscle spasms. **Analysis of Options:** * **Option A (Correct):** It acts on the CNS (spinal cord) to reduce spasticity. * **Option B (Incorrect):** Peripherally acting relaxants (e.g., Succinylcholine, Vecuronium) act at the Neuromuscular Junction (NMJ), not the spinal cord. * **Option C (Incorrect):** Baclofen does not have a direct clinical effect on the motor endplate or muscle fibers. * **Option D (Incorrect):** **Dantrolene** is the classic "direct-acting" muscle relaxant, as it acts on the Ryanodine receptors (RyR1) of the sarcoplasmic reticulum within the muscle cell. **High-Yield Clinical Pearls for NEET-PG:** * **Drug of Choice:** Baclofen is the preferred agent for treating spasticity associated with **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:** Abrupt discontinuation can lead to visual hallucinations, seizures, and rebound spasticity; it must be tapered gradually.

Q: Which of the following is NOT metabolized by cholinesterase?

Bupivacaine. ### Explanation The classification of local anesthetics (LAs) is a high-yield topic for NEET-PG. LAs are divided into two main groups based on their chemical linkage: **Esters** and **Amides**. **1. Why Bupivacaine is the Correct Answer:** Bupivacaine is an **Amide** local anesthetic. Amide LAs are primarily metabolized in the **liver** by microsomal enzymes (Cytochrome P450). They are not substrates for plasma cholinesterase. A simple mnemonic to identify amides is that their names contain two "i"s (e.g., Bup**i**vaca**i**ne, L**i**doca**i**ne, Pr**i**loca**i**ne, Rop**i**vaca**i**ne). **2. Analysis of Incorrect Options:** * **Tetracaine & Procaine (Options A & B):** These are **Ester** local anesthetics (containing only one "i" in their name). Esters are rapidly hydrolyzed by **pseudocholinesterase** (plasma cholinesterase). This results in a shorter half-life compared to amides. * **Acetylcholine (Option C):** This is a neurotransmitter that is rapidly degraded by both acetylcholinesterase (at the neuromuscular junction) and **butyrylcholinesterase** (plasma cholinesterase). **3. Clinical Pearls for NEET-PG:** * **Metabolism & Toxicity:** Patients with atypical pseudocholinesterase deficiency are at risk of prolonged effects/toxicity from ester LAs and Succinylcholine. * **Allergy:** Ester LAs are more likely to cause allergic reactions due to their metabolite, **Para-aminobenzoic acid (PABA)**. Amides rarely cause true allergies. * **Bupivacaine Specifics:** It is highly cardiotoxic (blocks sodium channels in the heart during diastole). **Intralipid (20%)** is the specific treatment for Local Anesthetic Systemic Toxicity (LAST). * **Cocaine:** The only ester LA that causes vasoconstriction (others are vasodilators).

Question 1

Which of the following statements regarding Phenytoin is FALSE?

Accepted Answer

At very low doses, zero-order kinetics occurs

Answer

Induces microsomal enzymes

Answer

Higher the dose, higher is the half-life

Answer

Highly protein-bound

Question 2

Amide type of local anesthetic agents undergo biotransformation primarily in which organ?

Accepted Answer

Liver

Answer

Kidney

Answer

Plasma

Answer

Excreted in unaltered form

Question 3

Which ester local anesthetic undergoes significant liver metabolism?

Accepted Answer

Cocaine

Answer

Tetracaine

Answer

Procaine

Answer

Chloroprocaine

Question 4

Which of the following statements is true regarding carbamazepine?

Accepted Answer

Used in the treatment of trigeminal neuralgia.

Answer

Carbamazepine is a potent enzyme inducer.

Answer

Can cause megaloblastic anemia.

Answer

It is the drug of choice for status epilepticus.

Question 5

D2 receptors are maximally seen in which area?

Accepted Answer

Corpus striatum

Answer

Frontal lobe

Answer

Nucleus accumbens

Answer

Cerebellum

Question 6

Levodopa is contraindicated in which of the following conditions?

Accepted Answer

Angle closure glaucoma

Answer

Hypertension

Answer

Multiple sclerosis

Answer

Pheochromocytoma

Question 7

Which of the following can be used in the treatment of myoclonic seizures, except?

Accepted Answer

Carbamazepine

Answer

Valproate

Answer

Topiramate

Answer

Zonisamide

Question 8

Valproic acid causes all EXCEPT-

Accepted Answer

It is an enzyme inducer

Answer

It causes obesity

Answer

It causes hirsutism

Answer

It causes neural tube defects

Question 9

What is the primary classification of Baclofen?

Accepted Answer

Centrally acting muscle relaxant

Answer

Peripherally acting muscle relaxant

Answer

Both centrally and peripherally acting muscle relaxant

Answer

Direct acting muscle relaxant

Question 10

Which of the following is NOT metabolized by cholinesterase?

Accepted Answer

Bupivacaine

Answer

Tetracaine

Answer

Procaine

Answer

Acetylcholine

Central Nervous System Pharmacology — MCQs

Central Nervous System Pharmacology — MCQs

On this page

Practice by Chapter

Want unlimited practice?