Central Nervous System Pharmacology Practice Questions

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.

Q: Which of the following is NOT a first-line choice drug for epilepsy in pregnancy?

Sodium valproate. ### Explanation **Sodium Valproate** is the correct answer because it is strictly contraindicated as a first-line agent in pregnancy due to its high **teratogenic potential**. It is associated with a significantly higher risk of major congenital malformations (MCMs) compared to other anti-epileptic drugs (AEDs). #### Why Sodium Valproate is avoided: * **Neural Tube Defects (NTDs):** It carries a 1–2% risk of spina bifida (due to interference with folate metabolism). * **Fetal Valproate Syndrome:** Characterized by craniofacial anomalies, cardiovascular defects, and limb abnormalities. * **Neurodevelopmental Delay:** Prenatal exposure is linked to lower IQ scores and increased risk of autism spectrum disorders in children. #### Why other options are incorrect: * **Lamotrigine (B) and Levetiracetam (C):** These are currently considered the **safest and preferred first-line choices** in pregnancy. They have the lowest reported rates of major malformations. * **Carbamazepine (A):** While it carries a slightly higher risk than Lamotrigine (specifically for cleft lip/palate), it is still significantly safer than Valproate and is considered a viable first-line option if the patient is already well-controlled on it. #### High-Yield Clinical Pearls for NEET-PG: 1. **Drug of Choice (DOC):** If a woman on Valproate plans pregnancy, she should be switched to **Levetiracetam** or **Lamotrigine** before conception. 2. **Folic Acid:** All pregnant women on AEDs should take high-dose folic acid (5 mg/day) to reduce NTD risks. 3. **Enzyme Inducers:** Carbamazepine and Phenytoin induce hepatic enzymes, which can lead to Vitamin K deficiency in the newborn; hence, Vitamin K prophylaxis is essential at birth. 4. **Monotherapy:** The gold standard for managing epilepsy in pregnancy is to use the **lowest effective dose** of a **single drug** (monotherapy).

Q: Which of the following conditions respond well with clonidine?

All of the above. **Explanation:** Clonidine is a centrally acting **$\alpha_2$-adrenergic agonist**. By stimulating presynaptic $\alpha_2$ receptors in the brainstem (specifically the vasomotor center and locus coeruleus), it reduces sympathetic outflow, leading to a decrease in peripheral resistance and heart rate. Beyond its use as an antihypertensive, its ability to modulate catecholamine release makes it effective in several neuropsychiatric conditions. * **Opiate Withdrawal:** Clonidine suppresses the sympathetic overactivity (tachycardia, hypertension, sweating, and anxiety) caused by the "noradrenergic storm" that occurs during opioid withdrawal. It is a standard non-opioid treatment for managing these autonomic symptoms. * **Attention-Deficit/Hyperactivity Disorder (ADHD):** It is used as a second-line or adjunctive treatment, particularly in children who do not tolerate stimulants or have comorbid tics. It works by modulating prefrontal cortex activity. * **Tourette’s Disorder:** Clonidine (and Guanfacine) are often preferred initial treatments for tics because they have a better side-effect profile compared to antipsychotics (haloperidol/pimozide). **Clinical Pearls for NEET-PG:** 1. **Rebound Hypertension:** Sudden withdrawal of clonidine can cause a hypertensive crisis due to a massive surge in catecholamines. 2. **Guanfacine:** A more selective $\alpha_{2A}$ agonist than clonidine, often preferred in ADHD due to less sedation and longer duration of action. 3. **Other Uses:** Clonidine is also used in the prophylaxis of **migraine**, treatment of **menopausal hot flashes**, and as a diagnostic test for **pheochromocytoma** (Clonidine Suppression Test). 4. **Side Effects:** Most common are sedation, xerostomia (dry mouth), and bradycardia.

Question 1

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 2

Adverse effects of valproic acid include:

Accepted Answer

All of the above

Answer

Alopecia

Answer

Fulminant hepatitis

Answer

Pancreatitis

Question 3

Side effects of diphenylhydantoin may include all except?

Accepted Answer

Inter-nuclear ophthalmoplegia

Answer

Gingival hyperplasia

Answer

Acute cerebellar syndrome

Answer

Megaloblastic anaemia

Question 4

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

Accepted Answer

Haloperidol

Answer

Valproate sodium

Answer

Carbamazepine

Answer

Phenytoin

Question 5

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 6

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 7

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.

Question 8

Which of the following is NOT a first-line choice drug for epilepsy in pregnancy?

Accepted Answer

Sodium valproate

Answer

Carbamazepine

Answer

Lamotrigine

Answer

Levetiracetam

Question 9

What is the most serious side effect of valproate?

Accepted Answer

Fulminant hepatitis

Answer

Spina bifida

Answer

Weight gain

Answer

Thrombocytopenia

Question 10

Which of the following conditions respond well with clonidine?

Accepted Answer

All of the above

Answer

Opiate withdrawal

Answer

Attention-deficit/hyperactivity disorder

Answer

Tourette's disorder

Central Nervous System Pharmacology — MCQs

Central Nervous System Pharmacology — MCQs

On this page

Practice by Chapter

Want unlimited practice?