Central Nervous System Pharmacology Practice Questions

Q: A patient with Parkinsonism is managed with levodopa. What happens if Vitamin B complex is administered concurrently to the patient?

Decreased efficacy will result.. The correct answer is **D. Decreased efficacy will result.** **Mechanism of Interaction:** Levodopa is a precursor to dopamine that must cross the blood-brain barrier (BBB) to be effective. In the periphery, levodopa is converted to dopamine by the enzyme **Dopa decarboxylase (DDC)** [1]. Vitamin B6 (Pyridoxine), a common component of Vitamin B complex, acts as a **cofactor** for DDC. When administered concurrently, Pyridoxine accelerates the peripheral decarboxylation of levodopa into dopamine. Since dopamine cannot cross the BBB, less levodopa remains available to enter the brain, leading to a significant reduction in therapeutic efficacy [1]. **Analysis of Incorrect Options:** * **Option A:** The action is not potentiated; it is diminished because the drug is "wasted" in the systemic circulation before reaching its target site. * **Option B:** Decarboxylation in the brain is not the primary issue; rather, it is the **increased peripheral decarboxylation** that prevents the drug from reaching the brain. * **Option C:** Side effects are actually **increased**. Higher peripheral dopamine levels lead to greater activation of systemic receptors, causing nausea, vomiting, and cardiac arrhythmias. **NEET-PG High-Yield Pearls:** * **The Carbidopa Solution:** Modern formulations combine Levodopa with **Carbidopa** (a peripheral DDC inhibitor). Carbidopa does not cross the BBB, so it prevents peripheral conversion but allows central conversion [1]. * **Pyridoxine Paradox:** The interaction between Vitamin B6 and Levodopa **does not occur** if the patient is taking the Levodopa-Carbidopa combination, as Carbidopa effectively blocks the Pyridoxine-enhanced peripheral metabolism. * **Dietary Advice:** Patients on plain Levodopa should be advised to avoid high-protein meals (which compete for transport) and excessive Pyridoxine intake.

Q: Hyponatremia is a known side effect of which of the following medications?

Carbamazepine. **Explanation:** **Carbamazepine** is a well-known cause of **hyponatremia** (occurring in up to 10-15% of patients). The underlying mechanism is the stimulation of **Antidiuretic Hormone (ADH)** release and the sensitization of renal tubules to ADH, leading to a condition similar to SIADH (Syndrome of Inappropriate Antidiuretic Hormone secretion). This effect is dose-dependent and more common in elderly patients or those taking concomitant diuretics. **Analysis of Incorrect Options:** * **Olanzapine (A):** An atypical antipsychotic primarily associated with metabolic side effects such as weight gain, dyslipidemia, and hyperglycemia. It does not typically cause electrolyte imbalances. * **Lithium (B):** Unlike Carbamazepine, Lithium is associated with **Hypernatremia**. It causes Nephrogenic Diabetes Insipidus (NDI) by antagonizing the effects of ADH on the collecting ducts, leading to polyuria and dilute urine. * **Clonazepam (D):** A benzodiazepine that acts on GABA-A receptors. Its primary side effects are sedation, ataxia, and cognitive impairment; it has no significant effect on sodium regulation. **High-Yield Clinical Pearls for NEET-PG:** * **Oxcarbazepine**, a derivative of carbamazepine, carries an even **higher risk** of hyponatremia. * **SSRIs** (e.g., Fluoxetine, Sertraline) are the most common class of psychotropic drugs associated with SIADH/hyponatremia in the elderly. * **Monitoring:** When prescribing Carbamazepine, baseline and periodic serum sodium levels should be checked, especially if the patient develops symptoms like confusion, lethargy, or seizures. * **HLA-B*1502:** Always screen for this allele in Asian populations before starting Carbamazepine to prevent Stevens-Johnson Syndrome (SJS).

Q: Which of the following is not a new drug for Migraine?

Romosozumab. **Explanation:** The correct answer is **Romosozumab** because it is not used for migraine; it is a monoclonal antibody used to treat **severe osteoporosis** in postmenopausal women at high risk of fracture. It works by inhibiting **sclerostin**, thereby increasing bone formation and decreasing bone resorption. **Analysis of Incorrect Options:** * **Lasmiditan:** This is a first-in-class **5-HT1F receptor agonist**. Unlike triptans (5-HT1B/1D), it lacks vasoconstrictive properties, making it a safe alternative for migraine patients with cardiovascular contraindications. * **Ubrogepant & Rimegepant:** These belong to the **"Gepants"** class. they are small-molecule **CGRP (Calcitonin Gene-Related Peptide) receptor antagonists** approved for the acute treatment of migraine. Rimegepant is unique as it is approved for both acute treatment and prevention. **High-Yield Clinical Pearls for NEET-PG:** 1. **CGRP Pathway:** This is the most important recent target in migraine pharmacology. * *Monoclonal Antibodies (mAbs) for Prophylaxis:* Erenumab (targets CGRP receptor); Fremanezumab, Galcanezumab, and Eptinezumab (target CGRP ligand). * *Small Molecules (Gepants) for Acute/Prophylaxis:* Ubrogepant, Rimegepant, Atogepant. 2. **Lasmiditan Side Effect:** The most common side effect is **dizziness/somnolence**; patients are advised not to drive for 8 hours after intake. 3. **Romosozumab Warning:** It carries a boxed warning for increased risk of myocardial infarction, stroke, and cardiovascular death.

Q: Which of the following statements is true regarding local anesthesia?

They are acidic salts of weak bases.. ### Explanation **1. Why Option D is Correct:** Local anesthetics (LAs) are chemically **weak bases**. In their pure alkaloid form, they are poorly soluble in water and unstable. To make them clinically useful, stable, and water-soluble for injection, they are combined with a strong acid (usually Hydrochloric Acid) to form **hydrochloride salts**. Therefore, the final injectable solution is an **acidic salt of a weak base** (typically with a pH of 5.0 to 6.0). **2. Analysis of Incorrect Options:** * **Option A:** This is chemically reversed. LAs are weak bases, not weak acids. * **Option B:** LAs are actually **more effective** in an alkaline pH. An alkaline environment increases the fraction of the non-ionized (lipid-soluble) form of the drug, which is essential for crossing the neuronal lipid membrane to reach the site of action. * **Option C:** While LAs do form salts with acids, Option D is the more precise chemical description required for pharmacological classification in competitive exams. **3. Clinical Pearls & High-Yield Facts for NEET-PG:** * **Mechanism of Action:** LAs block voltage-gated **Sodium (Na+) channels** from the *inside* of the cell membrane. * **The pH Paradox:** While the non-ionized form crosses the membrane, the **ionized (charged) form** is the one that actually binds to and blocks the receptor. * **Infected Tissues:** LAs work poorly in abscesses or infected tissues because the **acidic environment (low pH)** increases ionization, preventing the drug from crossing the nerve membrane. * **Bicarbonate Addition:** Adding Sodium Bicarbonate to LA (alkalinization) speeds up the onset of action by increasing the non-ionized fraction. * **Order of Blockade:** Pain > Temperature > Touch > Deep Pressure > Motor (Small myelinated fibers are blocked before large unmyelinated fibers).

Q: Adverse effects of valproic acid include:

All of the above. **Explanation:** Valproic acid (Sodium Valproate) is a broad-spectrum antiepileptic drug that acts by multiple mechanisms, including blocking voltage-gated sodium channels, increasing GABA levels, and inhibiting T-type calcium channels. While highly effective, it is associated with a distinct profile of adverse effects. **Analysis of Options:** * **A. Alopecia:** Valproate frequently causes dose-related hair thinning or loss (alopecia). Interestingly, when the hair regrows, it may become curly. * **B. Fulminant Hepatitis:** This is a rare but life-threatening idiosyncratic reaction. It is most common in children under two years of age, especially those on polytherapy or with underlying metabolic disorders. Monitoring Liver Function Tests (LFTs) is mandatory. * **C. Pancreatitis:** Acute pancreatitis is a serious, potentially fatal side effect of valproate that can occur at any time during treatment, regardless of the dose or duration. Since all three conditions are documented adverse effects, **Option D (All of the above)** is the correct answer. **High-Yield Clinical Pearls for NEET-PG:** * **Mnemonic (VALPROATE):** **V**omiting, **A**lopecia, **L**iver toxicity, **P**ancreatitis/PCOS, **R**etention of weight (Obesity), **O**edema, **A**teratogenicity (Neural Tube Defects), **T**remors, **E**nzyme inhibitor. * **Teratogenicity:** It is the most teratogenic antiepileptic, specifically causing **Spina Bifida** (Neural Tube Defects). * **Metabolism:** Unlike many other antiepileptics (like Phenytoin or Carbamazepine), Valproate is a **Microsomal Enzyme Inhibitor**. * **Drug of Choice:** It remains the first-line treatment for Generalized Tonic-Clonic Seizures (GTCS), Myoclonic seizures, and Absence seizures.

Q: Side effects of diphenylhydantoin may include all except?

Inter-nuclear ophthalmoplegia. **Explanation:** **Diphenylhydantoin (Phenytoin)** is a widely used hydantoin derivative for epilepsy. The correct answer is **Inter-nuclear ophthalmoplegia (INO)** because it is a localized brainstem lesion (typically involving the medial longitudinal fasciculus) most commonly associated with Multiple Sclerosis or strokes, not drug toxicity. **Why the other options are incorrect (Side effects of Phenytoin):** * **Gingival Hyperplasia:** A classic side effect occurring in ~20% of patients due to overgrowth of gum tissue (fibroblast proliferation). * **Acute Cerebellar Syndrome:** Phenytoin has a high affinity for the cerebellum. Toxicity manifests as **nystagmus**, ataxia, dysarthria, and diplopia. * **Megaloblastic Anaemia:** Phenytoin interferes with folate absorption and metabolism, leading to macrocytic anemia. **High-Yield Clinical Pearls for NEET-PG:** To remember the side effects of Phenytoin, use the mnemonic **"HOT MALAI"**: * **H** – Hirsutism, Hypertrophy of gums (Gingival hyperplasia) * **O** – Osteomalacia (due to Vitamin D metabolism interference) * **T** – Teratogenicity (**Fetal Hydantoin Syndrome**: cleft lip/palate, microcephaly) * **M** – Megaloblastic anemia * **A** – Ataxia (Cerebellar signs) * **L** – Lymphadenopathy (Pseudolymphoma) * **A** – Arrhythmias (when given as rapid IV bolus) * **I** – Insulin inhibition (leading to hyperglycemia) **Pharmacokinetics Note:** Phenytoin follows **Zero-order kinetics** (Capacity-limited metabolism) at therapeutic or high doses, meaning small dose increases can lead to disproportionate rises in plasma levels and toxicity.

Q: Which drug can be used in the management of Sydenham’s chorea?

Haloperidol. **Explanation:** **Sydenham’s chorea** is a major manifestation of Acute Rheumatic Fever, characterized by involuntary, purposeless movements caused by autoimmune-mediated inflammation of the basal ganglia. The pathophysiology involves **dopaminergic overactivity** in the nigrostriatal pathway. **Why Haloperidol is correct:** Haloperidol is a potent **D2 receptor antagonist** (typical antipsychotic). By blocking dopamine receptors in the striatum, it effectively suppresses choreiform movements. It is considered one of the first-line pharmacological treatments for severe Sydenham’s chorea when symptoms interfere with daily activities or safety. **Analysis of Incorrect Options:** * **Valproate sodium & Carbamazepine:** While Valproate is sometimes used as a second-line alternative (due to its GABAergic effects) if dopamine antagonists are contraindicated, **Haloperidol** remains the classic, more frequently tested answer for chorea management. Carbamazepine is primarily an antiepileptic and has no established role in treating chorea. * **Phenytoin:** This is an antiepileptic drug that can actually **induce or worsen** chorea as a side effect; therefore, it is contraindicated in this clinical scenario. **Clinical Pearls for NEET-PG:** * **First-line management:** Most cases of Sydenham’s chorea are self-limiting and require only bed rest and penicillin prophylaxis. * **Drug of choice for movement control:** Haloperidol or Pimozide (D2 blockers). * **Alternative:** Sodium Valproate is preferred by some clinicians to avoid the risk of Extrapyramidal Side Effects (EPS) associated with Haloperidol. * **Steroids:** May be used in refractory cases to hasten recovery due to the autoimmune nature of the disease.

Q: A 40-year-old patient with liver dysfunction is scheduled for a surgical procedure. Lorazepam can be used for pre-anaesthetic medication in this patient without concern for excessive CNS depression because the drug is:

Conjugated directly. **Explanation:** The correct answer is **B. Conjugated directly**. **Medical Concept:** Most benzodiazepines (like Diazepam and Midazolam) undergo **Phase I metabolism** (oxidation/reduction) via the Cytochrome P450 system in the liver before undergoing Phase II conjugation. In patients with liver dysfunction, Phase I reactions are significantly impaired, leading to the accumulation of active metabolites and prolonged CNS depression. **Lorazepam**, along with **Oxazepam** and **Temazepam** (remembered by the mnemonic **LOT**), bypasses Phase I metabolism. These drugs undergo direct **Phase II metabolism** (Glucuronidation) to form inactive, water-soluble metabolites that are excreted by the kidneys. Since Phase II metabolism is relatively preserved even in advanced liver disease, Lorazepam is the preferred benzodiazepine for patients with hepatic impairment. **Analysis of Incorrect Options:** * **A. Selective anxiolytic like buspirone:** Buspirone is a serotonin (5-HT1A) receptor agonist used for chronic anxiety; it is not used for pre-anaesthetic medication as it lacks immediate sedative effects. * **C. Reversible by naloxone:** Naloxone is a specific opioid antagonist. The specific antagonist for benzodiazepines is **Flumazenil**. * **D. Forming several active metabolites:** This is characteristic of drugs like Diazepam (which forms desmethyldiazepam). Active metabolites prolong the duration of action, which is exactly what we want to avoid in liver failure. **High-Yield NEET-PG Pearls:** * **LOT** (Lorazepam, Oxazepam, Temazepam) are safe in liver failure and in the elderly. * **Midazolam** is the most common pre-anaesthetic medication due to its rapid onset and potent anterograde amnesia, but it requires cautious dosing in hepatic failure. * **Phase II reactions** (Glucuronidation, Acetylation, Sulfonation) are generally "sturdier" and less affected by age or liver disease than Phase I reactions.

Q: Regarding lamotrigine, which of the following statements is true?

It is a broad spectrum antiepileptic drug.. **Explanation:** **Lamotrigine** is a versatile antiepileptic drug (AED) primarily known for its **broad-spectrum activity**. 1. **Why Option C is Correct:** Lamotrigine is effective against a wide variety of seizure types, including focal (partial) seizures and generalized seizures (tonic-clonic, absence, and myoclonic). Its primary mechanism involves **blocking voltage-gated sodium (Na+) channels** in their inactivated state, which inhibits the release of excitatory neurotransmitters like **glutamate**. 2. **Why Other Options are Incorrect:** * **Option A:** Lamotrigine has no significant dopaminergic activity and is not used to treat Parkinsonism. * **Option B:** While it reduces glutamate release, its primary molecular target is the **sodium channel**, not the NMDA receptor (unlike drugs like Memantine or Ketamine). * **Option C vs D:** Unlike older narrow-spectrum drugs (e.g., Phenytoin or Carbamazepine), which can exacerbate absence seizures, Lamotrigine is effective in treating **absence seizures**. **High-Yield Clinical Pearls for NEET-PG:** * **Stevens-Johnson Syndrome (SJS):** The most dreaded side effect of Lamotrigine is a severe skin rash (SJS/TEN). To minimize this risk, the drug must be started at a low dose and **titrated very slowly**. * **Bipolar Disorder:** Beyond epilepsy, it is a first-line agent for the **maintenance treatment of Bipolar Depression**. * **Pregnancy:** It is considered one of the **safer AEDs during pregnancy** (lower teratogenic risk compared to Valproate), though clearance increases significantly during gestation. * **Drug Interaction:** Valproate inhibits Lamotrigine metabolism, doubling its half-life and significantly increasing the risk of life-threatening rashes.

Question 1

A patient with Parkinsonism is managed with levodopa. What happens if Vitamin B complex is administered concurrently to the patient?

Accepted Answer

Decreased efficacy will result.

Answer

The action of levodopa in the brain will be potentiated.

Answer

Decarboxylation of levodopa in the brain will be decreased.

Answer

Side effects will be ameliorated.

Question 2

Hyponatremia is a known side effect of which of the following medications?

Accepted Answer

Carbamazepine

Answer

Olanzapine

Answer

Lithium

Answer

Clonazepam

Question 3

Which of the following is not a new drug for Migraine?

Accepted Answer

Romosozumab

Answer

Lasmiditan

Answer

Ubrogepant

Answer

Rimegepant

Question 4

Which of the following statements is true regarding local anesthesia?

Accepted Answer

They are acidic salts of weak bases.

Answer

They are basic salts of weak acids.

Answer

They are not effective in alkaline pH.

Answer

They form salts with acids.

Question 5

Adverse effects of valproic acid include:

Accepted Answer

All of the above

Answer

Alopecia

Answer

Fulminant hepatitis

Answer

Pancreatitis

Question 6

Side effects of diphenylhydantoin may include all except?

Accepted Answer

Inter-nuclear ophthalmoplegia

Answer

Gingival hyperplasia

Answer

Acute cerebellar syndrome

Answer

Megaloblastic anaemia

Question 7

Which drug can be used in the management of Sydenham’s chorea?

Accepted Answer

Haloperidol

Answer

Valproate sodium

Answer

Carbamazepine

Answer

Phenytoin

Question 8

Local anesthetics cannot be used at the site of infection because it causes:

Accepted Answer

Both

Answer

Spread of infection

Answer

Lowered efficiency

Answer

None

Question 9

A 40-year-old patient with liver dysfunction is scheduled for a surgical procedure. Lorazepam can be used for pre-anaesthetic medication in this patient without concern for excessive CNS depression because the drug is:

Accepted Answer

Conjugated directly

Answer

Selective anxiolytic like buspirone

Answer

Reversible by administration of naloxone

Answer

Forming several active metabolites

Question 10

Regarding lamotrigine, which of the following statements is true?

Accepted Answer

It is a broad spectrum antiepileptic drug.

Answer

It is a dopaminergic agonist used in Parkinsonism.

Answer

It acts by blocking NMDA type of glutamate receptors.

Answer

It suppresses tonic-clonic seizures but worsens absence seizures.

Central Nervous System Pharmacology — MCQs

Central Nervous System Pharmacology — MCQs

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