Central Nervous System Pharmacology Practice Questions

Q: What is the drug of choice for myoclonic epilepsy in pregnancy?

Sodium valproate. **Explanation:** The drug of choice for **myoclonic epilepsy** (such as Juvenile Myoclonic Epilepsy) is **Sodium Valproate** [1]. It is a broad-spectrum antiepileptic that works by increasing GABA levels, blocking voltage-gated sodium channels, and inhibiting T-type calcium channels. While Valproate is generally avoided in pregnancy due to its high teratogenic potential (Neural Tube Defects) [2], it remains the **drug of choice for myoclonic seizures** because other agents are often ineffective or may even exacerbate this specific seizure type [1]. In clinical practice, if a patient is well-controlled on Valproate, the dose is minimized and supplemented with high-dose Folic Acid (5mg). **Why the other options are incorrect:** * **Carbamazepine:** It is the drug of choice for focal (partial) seizures [1] and trigeminal neuralgia. However, it is contraindicated in myoclonic seizures as it can **worsen** them. * **Phenobarbitone:** While used in neonatal seizures and status epilepticus, it is not the first-line agent for myoclonic epilepsy and is associated with significant sedation and cognitive side effects. * **Phenytoin:** Similar to Carbamazepine, Phenytoin is effective for generalized tonic-clonic and focal seizures [1] but can aggravate myoclonic and absence seizures. **High-Yield NEET-PG Pearls:** * **Teratogenicity:** Valproate is the most teratogenic AED (causes **Spina Bifida**) [2]. * **Safest in Pregnancy:** **Levetiracetam** and **Lamotrigine** are generally considered the safest AEDs during pregnancy. * **DOC for Absence Seizures:** Ethosuximide (Valproate is second line). * **DOC for Infantile Spasms:** Vigabatrin (in Tuberous Sclerosis) or ACTH.

Q: What is a specific inhibitor of alcohol dehydrogenase?

Fomepizole. **Explanation:** The metabolism of alcohols (Ethanol, Methanol, and Ethylene glycol) primarily occurs in the liver via two main enzymes: **Alcohol Dehydrogenase (ADH)** and **Aldehyde Dehydrogenase (ALDH)**. **1. Why Fomepizole is correct:** **Fomepizole** is a potent, competitive inhibitor of **Alcohol Dehydrogenase (ADH)**. By blocking this enzyme, it prevents the conversion of Methanol and Ethylene glycol into their toxic metabolites (Formaldehyde/Formic acid and Glycolic/Oxalic acid, respectively). It is the preferred antidote for Methanol and Ethylene glycol poisoning because it prevents metabolic acidosis and end-organ damage (like blindness or renal failure). **2. Why other options are incorrect:** * **Disulfiram:** It inhibits **Aldehyde Dehydrogenase (ALDH)**. This leads to the accumulation of Acetaldehyde if ethanol is consumed, causing the "Disulfiram-like reaction" (flushing, tachycardia, nausea). It is used in aversion therapy for chronic alcoholism. * **Methyl alcohol:** This is a substrate for ADH, not an inhibitor. It is metabolized into toxic formic acid. * **Zolpidem:** This is a non-benzodiazepine hypnotic (Z-drug) that acts on the $GABA_A$ receptor. It has no effect on alcohol-metabolizing enzymes. **High-Yield Clinical Pearls for NEET-PG:** * **Methanol Poisoning:** Characterized by "snowstorm vision" and optic disc hyperemia. * **Ethylene Glycol Poisoning:** Characterized by calcium oxalate crystals in urine (envelope-shaped) and acute tubular necrosis. * **Alternative Treatment:** If Fomepizole is unavailable, **Ethanol** can be used as an antidote because it has a higher affinity for ADH than methanol, acting as a competitive substrate. * **Cofactor:** Ethanol metabolism follows **zero-order kinetics** and requires $NAD^+$ as a cofactor.

Q: Which of the following drugs can cause toxic epidermal necrolysis as an adverse effect?

Lamotrigine. **Explanation:** **Lamotrigine** is a broad-spectrum antiepileptic drug (AED) that acts by blocking voltage-gated sodium channels and inhibiting glutamate release. Its most significant and life-threatening adverse effect is a severe hypersensitivity reaction manifesting as **Stevens-Johnson Syndrome (SJS)** or **Toxic Epidermal Necrolysis (TEN)**. The risk is highest during the first 8 weeks of treatment and is significantly increased if the drug is started at a high dose or escalated rapidly. **Analysis of Options:** * **Lamotrigine (Correct):** Known for causing severe skin rashes. To minimize this risk, clinicians follow a "low and slow" titration schedule. * **Felbamate:** Primarily associated with **aplastic anemia** and **severe hepatotoxicity**, which limits its clinical use. * **Gabapentin:** Generally well-tolerated; its main side effects are sedation, dizziness, and peripheral edema. It is not typically associated with life-threatening dermatological reactions. * **Vigabatrin:** Notorious for causing **permanent visual field defects** (concentric contraction) due to retinal toxicity, requiring regular perimetry monitoring. **High-Yield Clinical Pearls for NEET-PG:** * **Drug Interaction:** Valproate inhibits the metabolism of Lamotrigine, doubling its half-life and significantly increasing the risk of SJS/TEN. * **Other Drugs causing SJS/TEN:** Remember the mnemonic **SAPP**: **S**ulfonamides, **A**ntiepileptics (Phenytoin, Carbamazepine, Phenobarbital, Lamotrigine), **P**enicillins, and **P**iroxicam (NSAIDs). * **HLA Link:** HLA-B*1502 is strongly associated with SJS/TEN caused by Carbamazepine, particularly in Asian populations.

Q: Which of the following local anesthetics is most cardiotoxic?

Bupivacaine. **Explanation:** **Bupivacaine** is the most cardiotoxic local anesthetic among the commonly used clinical agents. Its high lipid solubility and high affinity for voltage-gated sodium channels in the myocardium lead to a "slow-in, slow-out" phenomenon. Unlike Lignocaine, Bupivacaine dissociates very slowly from cardiac sodium channels during diastole, leading to a cumulative blockade. This results in severe ventricular arrhythmias (like Torsades de Pointes), negative inotropy, and refractory cardiac arrest that is notoriously difficult to resuscitate. **Analysis of Incorrect Options:** * **A. Dibucaine:** While it is a potent amide anesthetic, it is primarily used for its "Dibucaine Number" to identify atypical pseudocholinesterase. It is not the most cardiotoxic in clinical practice. * **C. Lignocaine:** It is the prototype amide anesthetic with a "fast-in, fast-out" profile. It is actually used as an anti-arrhythmic (Class Ib) and has a much higher safety margin regarding cardiac toxicity compared to Bupivacaine. * **D. Chloroprocaine:** An ester-linked anesthetic with a very short half-life due to rapid metabolism by plasma cholinesterases. It has the lowest potential for systemic toxicity. **High-Yield Clinical Pearls for NEET-PG:** * **CC/CNS Ratio:** Bupivacaine has a low ratio (approx. 3.0), meaning the dose required to cause cardiovascular collapse (CC) is close to the dose that causes CNS seizures, leaving a narrow safety margin. * **Antidote:** Intravenous **Lipid Emulsion (20% Intralipid)** is the specific treatment for Local Anesthetic Systemic Toxicity (LAST). * **S-Enantiomers:** Levobupivacaine and Ropivacaine were developed as safer alternatives to Bupivacaine, as they exhibit significantly less cardiotoxicity. * **Pregnancy:** Bupivacaine cardiotoxicity is enhanced in pregnancy due to progesterone-induced sensitivity.

Q: Carbamazepine is the drug of choice in which of the following seizure types?

Partial complex seizures. **Carbamazepine (CBZ)** is a first-line antiepileptic drug primarily used for focal (partial) seizures. Its mechanism of action involves blocking **voltage-gated sodium channels** in their inactivated state, which prevents high-frequency repetitive firing of action potentials [1, 2].**Why Option B is Correct:**Carbamazepine is considered the **Drug of Choice (DOC)** for **Partial (Focal) seizures**, including both simple and complex partial seizures, as well as Generalized Tonic-Clonic Seizures (GTCS). It is highly effective in stabilizing neuronal membranes against focal discharges [1, 2].**Why Other Options are Incorrect:** * **A. Absence Seizures:** Carbamazepine is contraindicated here as it can **exacerbate** absence seizures [2]. The DOC for absence seizures is Ethosuximide (or Valproate) [2]. * **C. Myoclonus:** Similar to absence seizures, Carbamazepine can worsen myoclonic jerks. The DOC for myoclonic seizures is Sodium Valproate. * **D. Infantile Spasms:** The DOC for infantile spasms (West Syndrome) is **ACTH** or Vigabatrin (especially if associated with Tuberous Sclerosis).**High-Yield Clinical Pearls for NEET-PG:** * **Trigeminal Neuralgia:** Carbamazepine is the specific **Drug of Choice** for this condition [1]. * **Auto-induction:** It induces its own metabolism (CYP3A4 induction), requiring dosage adjustments after the first few weeks of therapy. * **Side Effects:** Look for keywords like **Diplopia**, Ataxia, **SIADH** (Hyponatremia), and serious skin reactions like **Stevens-Johnson Syndrome** (associated with the HLA-B*1502 allele). * **Teratogenicity:** It can cause Neural Tube Defects (Spina Bifida).

Q: Carbidopa is used in the treatment of Parkinsonism because:

It decreases peripheral utilization of L-dopa. **Explanation:** **Why Option B is Correct:** Levodopa (L-dopa) is a precursor to dopamine that can cross the blood-brain barrier (BBB). However, when administered alone, more than 95% of L-dopa is decarboxylated into dopamine in the peripheral tissues by the enzyme **Peripheral Dopa Decarboxylase**. Since dopamine itself cannot cross the BBB, this peripheral conversion leads to systemic side effects (nausea, vomiting, cardiac arrhythmias) and reduces the amount of drug available to reach the brain. **Carbidopa** is a peripheral dopa decarboxylase inhibitor. It does not cross the BBB; therefore, it prevents the peripheral breakdown of L-dopa, increasing its bioavailability in the CNS and allowing for a dose reduction of L-dopa by about 75-80%. **Why Other Options are Incorrect:** * **Option A:** Carbidopa has no intrinsic pharmacological activity on dopamine receptors; it is an enzyme inhibitor, not an agonist. * **Option C:** Carbidopa *inhibits* the breakdown (decarboxylation) of L-dopa; it does not increase it. * **Option D:** Carbidopa actually *facilitates* more L-dopa entering the brain by ensuring it remains intact in the systemic circulation. It does not cross the BBB itself. **High-Yield Clinical Pearls for NEET-PG:** * **The "Sinemet" Combination:** The standard ratio of Levodopa to Carbidopa is usually **4:1 or 10:1**. * **Side Effects:** While Carbidopa reduces systemic side effects (nausea/vomiting), it may actually **accentuate central side effects** like dyskinesias and hallucinations because more dopamine is being produced in the brain. * **Pyridoxine (Vitamin B6) Interaction:** Pyridoxine is a cofactor that increases peripheral decarboxylation of L-dopa. Carbidopa nullifies this interaction, making it safe to take B6 with the combination therapy.

Q: All of the following drugs act by blocking AMPA receptors of glutamate except?

Felbamate. **Explanation:** The question tests your knowledge of the specific molecular targets of anti-epileptic drugs (AEDs) acting on the glutamatergic system. **1. Why Felbamate is the Correct Answer:** Felbamate primarily acts as a potent antagonist at the **NMDA (N-methyl-D-aspartate)** receptor, specifically binding to the glycine site. While it has multiple mechanisms (including modulation of $GABA_A$ receptors), it does **not** have a significant inhibitory effect on AMPA receptors. Therefore, it is the "except" in this list. **2. Analysis of Incorrect Options (Drugs that DO block AMPA):** * **Perampanel:** This is a highly selective, **non-competitive AMPA receptor antagonist**. It is the prototype drug for this mechanism and is high-yield for exams. * **Topiramate:** This is a broad-spectrum AED. One of its multiple mechanisms of action includes the blockade of the **AMPA/Kainate** subtype of glutamate receptors. * **Phenobarbitone:** While primarily known as a $GABA_A$ facilitator (increasing the duration of chloride channel opening), at higher therapeutic concentrations, it also **suppresses glutamate release** by inhibiting AMPA receptors. **Clinical Pearls for NEET-PG:** * **Perampanel Side Effect:** It carries a "Black Box Warning" for serious neuropsychiatric events (aggression, anger, and suicidal ideation). * **Topiramate "Mnemonic":** Remember it as the "5-in-1" drug: 1. Blocks Na+ channels, 2. Blocks Ca2+ channels, 3. Increases GABA, 4. Blocks AMPA, 5. Carbonic anhydrase inhibition (leads to weight loss and kidney stones). * **NMDA vs. AMPA:** Most older AEDs target NMDA or GABA; Perampanel is unique as the primary AMPA-specific blocker.

Q: Which of the following is NOT a property of local anesthetics?

Have high affinity for channels in the resting state.. **Explanation:** Local anesthetics (LAs) work by blocking voltage-gated sodium channels on the neuronal membrane, preventing the influx of sodium ions and the subsequent generation of an action potential. **1. Why Option B is the Correct Answer (The "Not" Property):** Local anesthetics exhibit **"use-dependent" or "state-dependent" blockade.** They have a much higher affinity for sodium channels when they are in the **open** or **inactivated** states (active firing). They have the **lowest affinity for the resting state.** This is why rapidly firing nerves (like those carrying pain signals) are blocked more effectively than resting nerves. **2. Analysis of Other Options:** * **Option A:** This is a true property. LAs preferentially bind to open and inactivated states, which is the basis of the modulated receptor hypothesis. * **Option C:** LAs are chemically **weak bases**, typically consisting of a lipophilic aromatic ring and a hydrophilic tertiary amine connected by an ester or amide link. * **Option D:** LAs exist in equilibrium between an uncharged base (B) and a charged cation (BH+). Only the uncharged base can cross the lipid membrane. In a **low pH environment (e.g., infected/inflamed tissue)**, the equilibrium shifts toward the ionized form, which cannot cross the membrane, making the LA **less effective.** **High-Yield Clinical Pearls for NEET-PG:** * **Order of Blockade:** Small myelinated fibers (Aδ) and unmyelinated fibers (C) are blocked before large myelinated fibers. Functionally: **Pain > Temperature > Touch > Pressure > Motor.** * **Bupivacaine:** Most cardiotoxic LA; treated with **Intralipid (20% lipid emulsion).** * **Cocaine:** The only LA with intrinsic vasoconstrictive properties. * **Benzocaine/Prilocaine:** Associated with the development of **Methemoglobinemia.**

Q: Which of the following anti-Parkinson drugs has the potential to cause retroperitoneal fibrosis?

Bromocriptine. **Explanation:** **Bromocriptine** is the correct answer because it belongs to the **Ergot-derivative** class of dopamine agonists. Ergot derivatives (which also include Pergolide and Cabergoline) are known to cause **fibrotic complications** such as retroperitoneal, pleuropulmonary, and cardiac valvular fibrosis. This is thought to be mediated by the activation of **5-HT2B receptors**, which stimulates fibroblast proliferation. Due to these serious side effects, the use of ergot-derived agonists has largely been superseded by non-ergot compounds. **Analysis of Incorrect Options:** * **Pramipexole (A) and Ropinirole (D):** These are **Non-ergot** dopamine agonists. They are preferred in clinical practice because they do not cause fibrotic complications. Their side effect profile typically includes impulse control disorders (pathological gambling), sleep attacks, and nausea. * **Entacapone (B):** This is a peripheral **COMT inhibitor** used as an adjunct to Levodopa to prevent its peripheral metabolism. Its characteristic side effect is orange discoloration of urine, not fibrosis. **NEET-PG High-Yield Pearls:** * **Fibrosis Rule:** If a dopamine agonist is an "Ergot" derivative, think of "Fibrosis." * **Pramipexole** is specifically noted for its antioxidant properties and is excreted unchanged in the urine (requires dose adjustment in renal failure). * **Apomorphine** is the dopamine agonist used as a "rescue" therapy for "off" episodes in Parkinson’s disease, administered subcutaneously. * **Impulse Control Disorders** (hypersexuality, gambling) are most strongly associated with the non-ergot agonists (Pramipexole, Ropinirole).

Question 1

What is the drug of choice for myoclonic epilepsy in pregnancy?

Accepted Answer

Sodium valproate

Answer

Carbamazepine

Answer

Phenobarbitone

Answer

Phenytoin

Question 2

What is a specific inhibitor of alcohol dehydrogenase?

Accepted Answer

Fomepizole

Answer

Disulfiram

Answer

Methyl alcohol

Answer

Zolpidem

Question 3

Which of the following drugs can cause toxic epidermal necrolysis as an adverse effect?

Accepted Answer

Lamotrigine

Answer

Felbamate

Answer

Gabapentin

Answer

Vigabatrin

Question 4

Which of the following local anesthetics is most cardiotoxic?

Accepted Answer

Bupivacaine

Answer

Dibucaine

Answer

Lignocaine

Answer

Chloroprocaine

Question 5

Carbamazepine is the drug of choice in which of the following seizure types?

Accepted Answer

Partial complex seizures

Answer

Absence seizures

Answer

Myoclonus

Answer

Infantile spasms

Question 6

Carbidopa is used in the treatment of Parkinsonism because:

Accepted Answer

It decreases peripheral utilization of L-dopa

Answer

It is a dopamine agonist

Answer

It increases the breakdown of L-dopa

Answer

It prevents the crossing of L-dopa into the brain

Question 7

A client with a subarachnoid hemorrhage is prescribed a 1,000-mg loading dose of Dilantin IV. Which consideration is most important when administering this dose?

Accepted Answer

Rapid Dilantin administration can cause cardiac arrhythmias.

Answer

Therapeutic drug levels should be maintained between 20 to 30 mg/ml.

Answer

Dilantin should be mixed in dextrose in water before administration.

Answer

Dilantin should be administered through an IV catheter in the client’s hand.

Question 8

All of the following drugs act by blocking AMPA receptors of glutamate except?

Accepted Answer

Felbamate

Answer

Perampanel

Answer

Phenobarbitone

Answer

Topiramate

Question 9

Which of the following is NOT a property of local anesthetics?

Accepted Answer

Have high affinity for channels in the resting state.

Answer

Preferentially bind to sodium channels in open and inactivated states.

Answer

They are weak bases.

Answer

Less effective in an environment with low extracellular pH.

Question 10

Which of the following anti-Parkinson drugs has the potential to cause retroperitoneal fibrosis?

Accepted Answer

Bromocriptine

Answer

Pramipexole

Answer

Entacapone

Answer

Ropinirole

Central Nervous System Pharmacology — MCQs

Central Nervous System Pharmacology — MCQs

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