Central Nervous System Pharmacology — MCQs

Central Nervous System Pharmacology Indian Medical PG Practice Questions and MCQs

Question 321: The following symptoms may be seen in opium withdrawal:

A. Constipation (Correct Answer)
B. Lacrimation
C. Dry nose and mouth
D. Constipation

Explanation: **Explanation:** Opioid withdrawal syndrome is characterized by a "rebound" effect of the sympathetic nervous system and the gastrointestinal tract, essentially presenting as the physiological opposite of acute opioid effects. **1. Why the Correct Answer is Right:** Opioids are notorious for causing **constipation** by decreasing intestinal motility and increasing sphincter tone. During withdrawal, the body experiences a rebound increase in peristalsis, leading to **diarrhea**, abdominal cramps, and hyperactive bowel sounds. Therefore, constipation is a feature of opioid *use/intoxication*, not withdrawal. *(Note: In the provided options, "Constipation" is marked as the correct answer, likely implying it is the "except" or "not seen" feature in a typical "all are seen except" question format common in NEET-PG.)* **2. Analysis of Other Options:** * **Lacrimation (Option B):** This is a classic early sign of opioid withdrawal. It occurs due to autonomic hyperactivity. * **Dry nose and mouth (Option C):** This is incorrect in the context of withdrawal. Withdrawal actually causes **rhinorrhea** (runny nose) and excessive salivation/sweating (wet symptoms). * **Option D:** Repeated as constipation. **3. High-Yield Clinical Pearls for NEET-PG:** * **The "Wet" Syndrome:** Remember opioid withdrawal as a "leaky" state—Lacrimation, Rhinorrhea, Diarrhea, Sweating (Diaphoresis), and Salivation. * **Mydriasis:** While opioids cause "pinpoint pupils" (Miosis), withdrawal causes **Mydriasis** (dilated pupils). * **Piloerection:** The appearance of "goosebumps" (cold turkey) is a highly specific sign of severe opioid withdrawal. * **Management:** **Clonidine** (alpha-2 agonist) is used to suppress autonomic overactivity; **Methadone** or **Buprenorphine** are used for substitution therapy. * **Vital Signs:** Look for tachycardia, hypertension, and insomnia in clinical vignettes.

Question 322: Which of the following drugs is NOT used in the management of alcohol withdrawal?

A. Naltrexone
B. Naloxone (Correct Answer)
C. Acamprosate
D. Disulfiram

Explanation: ### Explanation The management of Alcohol Use Disorder (AUD) is divided into two phases: **Acute Withdrawal** and **Relapse Prevention (Maintenance)**. **Why Naloxone is the Correct Answer:** Naloxone is a competitive **opioid antagonist** with a very short half-life, used primarily for the emergency reversal of **acute opioid overdose**. It has no role in the management of alcohol withdrawal or the long-term treatment of alcoholism. Unlike Naltrexone, it is not effective orally due to high first-pass metabolism. **Analysis of Incorrect Options:** * **Naltrexone (Option A):** An oral opioid antagonist that reduces alcohol cravings and the "reward" feeling by blocking mu-opioid receptors. It is a first-line agent for **relapse prevention**. * **Acamprosate (Option B):** A NMDA receptor antagonist and GABA-A agonist. It helps maintain abstinence by reducing the "negative affect" (insomnia, anxiety) associated with post-withdrawal. It is preferred in patients with **liver disease** (as it is renally excreted). * **Disulfiram (Option D):** An aldehyde dehydrogenase inhibitor. It causes the accumulation of acetaldehyde if alcohol is consumed, leading to an unpleasant "disulfiram-like reaction" (flushing, tachycardia, nausea). It acts as a **psychological deterrent**. **High-Yield Clinical Pearls for NEET-PG:** * **Drug of Choice (DOC) for Acute Alcohol Withdrawal:** Benzodiazepines (e.g., Chlordiazepoxide or Diazepam) to prevent seizures and delirium tremens. * **DOC for Alcoholism in Liver Failure:** Acamprosate (Naltrexone and Disulfiram are hepatotoxic). * **Wernicke’s Encephalopathy:** Always administer **Thiamine (B1)** before Glucose to prevent precipitating acute neurological deterioration. * **Naltrexone** is contraindicated in patients currently using opioids or those in acute opioid withdrawal.

Question 323: What is produced by the supersensitivity of Dopamine receptors?

A. Dyskinesia (Correct Answer)
B. Hyperphagia
C. Hyperpathia
D. Hypomania

Explanation: **Explanation:** The correct answer is **Dyskinesia**. This phenomenon is primarily explained by the concept of **Denervation Supersensitivity**. **1. Why Dyskinesia is correct:** When dopamine receptors (specifically in the nigrostriatal pathway) are chronically blocked by antipsychotics or deprived of dopamine (as in Parkinson’s disease), the postsynaptic neurons compensate by increasing the number and sensitivity of dopamine receptors (**upregulation**). When these "supersensitive" receptors are subsequently exposed to dopamine (either endogenous or via L-Dopa therapy), they overreact, leading to involuntary, purposeless movements known as **Dyskinesia**. A classic clinical example is **Tardive Dyskinesia**, which occurs after long-term use of typical antipsychotics. **2. Why other options are incorrect:** * **Hyperphagia:** This refers to excessive hunger. While dopamine is involved in reward circuits, hyperphagia is more closely linked to hypothalamic dysfunction or serotonin/leptin imbalances. * **Hyperpathia:** This is a clinical symptom where a painful stimulus evokes an exaggerated pain response. it is associated with neuropathic pain syndromes or thalamic lesions, not dopamine receptor sensitivity. * **Hypomania:** This is a mood state characterized by persistent disinhibition and elevation. While dopamine overactivity is linked to mania, it is a complex psychiatric state involving multiple neurotransmitters, not a direct result of receptor supersensitivity. **High-Yield Clinical Pearls for NEET-PG:** * **Tardive Dyskinesia (TD):** Characterized by orofacial movements (grimacing, tongue protrusion). It is often irreversible even after stopping the offending drug. * **Drug-Induced Parkinsonism:** Caused by receptor *blockade*; **Tardive Dyskinesia:** Caused by receptor *supersensitivity*. * **Management of TD:** Switching to atypical antipsychotics (like Clozapine) or using VMAT-2 inhibitors (Valbenazine, Deutetrabenazine). Avoid anticholinergics, as they can worsen TD.

Question 324: In patient-controlled analgesia, morphine is commonly given by which route?

A. Intravenous (Correct Answer)
B. Intramuscular
C. Subcutaneous
D. Sublingual

Explanation: **Explanation:** **Patient-Controlled Analgesia (PCA)** is a delivery system that allows patients to self-administer small, predetermined doses of analgesics (usually opioids) to manage acute pain. **Why Intravenous (IV) is the Correct Answer:** The **Intravenous route** is the gold standard and most common route for PCA. It is preferred because it offers the **fastest onset of action** (rapid peak effect) and **predictable bioavailability**. This allows the patient to achieve immediate relief during "breakthrough" pain episodes. The rapid titration possible with IV delivery ensures that the plasma concentration remains within the "narrow therapeutic window"—above the minimum effective concentration but below the level causing respiratory depression. **Why Other Options are Incorrect:** * **Intramuscular (IM):** This route is avoided in PCA because absorption is erratic, painful, and slow. It does not allow for the rapid dose-adjustment required for effective self-management. * **Subcutaneous (SC):** While sometimes used in palliative care (CADD pumps), it is not the standard for acute PCA due to slower absorption compared to IV and the risk of local tissue irritation or sterile abscesses with repeated boluses. * **Sublingual:** This route lacks the precision and automated lockout mechanisms inherent to electronic PCA pumps, making it unsuitable for controlled, demand-based dosing in a hospital setting. **High-Yield Clinical Pearls for NEET-PG:** * **Lockout Interval:** A safety feature in PCA pumps that prevents the patient from administering a second dose until a specific time has passed, reducing the risk of overdose. * **Drug of Choice:** **Morphine** is the most common, but **Fentanyl** is preferred in patients with renal failure (due to the accumulation of morphine’s active metabolite, Morphine-6-glucuronide). * **Monitoring:** The most critical parameter to monitor in a patient on PCA morphine is the **Respiratory Rate**, as opioid-induced respiratory depression is the most serious side effect.

Question 325: Which of the following is not an opioid peptide?

A. Beta endorphin
B. Epinephrine (Correct Answer)
C. Leu5-enkephalin
D. Met5-enkephalin

Explanation: **Explanation:** The correct answer is **Epinephrine** because it is a catecholamine neurotransmitter and hormone, not an opioid peptide. **1. Why Epinephrine is the correct answer:** Opioid peptides are specific chains of amino acids that act on opioid receptors ($\mu, \delta, \kappa$) to modulate pain and reward pathways. **Epinephrine** (Adrenaline) is derived from the amino acid tyrosine but is classified as a **catecholamine**. It acts on adrenergic receptors ($\alpha$ and $\beta$) and is primarily involved in the "fight or flight" sympathetic response, rather than the endogenous opioid system. **2. Analysis of incorrect options:** * **Beta-endorphin:** This is a potent endogenous opioid peptide derived from the precursor protein **Pro-opiomelanocortin (POMC)**. It has a high affinity for $\mu$-opioid receptors. * **Leu5-enkephalin and Met5-enkephalin:** These are pentapeptides (containing leucine or methionine at the 5th position) derived from **Pro-enkephalin A**. They are the primary endogenous ligands for $\delta$-opioid receptors and play a significant role in pain modulation. **3. NEET-PG Clinical Pearls & High-Yield Facts:** * **Precursors:** Remember the three main families of endogenous opioids and their precursors: 1. **Enkephalins** $\rightarrow$ Pro-enkephalin A 2. **Endorphins** $\rightarrow$ POMC (Pro-opiomelanocortin) 3. **Dynorphins** $\rightarrow$ Pro-enkephalin B (Prodynorphin) * **Receptor Selectivity:** Endorphins ($\mu$ > $\delta$), Enkephalins ($\delta$ > $\mu$), Dynorphins ($\kappa$). * **Shared Sequence:** Almost all endogenous opioid peptides share the same N-terminal tetrapeptide sequence: **Tyr-Gly-Gly-Phe**. This is essential for binding to opioid receptors.

Question 326: Which of the following drugs has the least extrapyramidal side effects?

A. Haloperidol
B. Fluphenazine
C. Clozapine (Correct Answer)
D. Flupenthioxol

Explanation: **Explanation:** The occurrence of Extrapyramidal Side Effects (EPS) in antipsychotic therapy is primarily linked to the blockade of **D2 receptors** in the nigrostriatal pathway. **Why Clozapine is correct:** Clozapine is the prototype **Atypical Antipsychotic (Second Generation)**. It has a unique receptor binding profile characterized by a **low affinity for D2 receptors** and a high affinity for 5-HT2A receptors. Additionally, it possesses potent **anticholinergic activity**, which inherently counteracts the development of EPS. Because it dissociates rapidly from D2 receptors ("loose binding"), it rarely causes dystonia, akathisia, or parkinsonism, making it the drug with the least EPS among the options. **Why the other options are incorrect:** * **Haloperidol & Fluphenazine:** These are **High-Potency Typical Antipsychotics**. They bind very tightly to D2 receptors and have minimal anticholinergic activity, resulting in the highest incidence of EPS (especially acute dystonia and parkinsonism). * **Flupenthioxol:** This is a thioxanthene derivative (Typical Antipsychotic). While slightly different in structure, it remains a potent D2 blocker with a significant risk of EPS compared to atypical agents. **High-Yield Clinical Pearls for NEET-PG:** * **Clozapine** is the "Gold Standard" for **Treatment-Resistant Schizophrenia**. * **Adverse Effects:** While it has the least EPS, it is notorious for **Agranulocytosis** (requires mandatory WBC monitoring), seizures (dose-dependent), myocarditis, and significant weight gain. * **Quetiapine** is another atypical antipsychotic with very low EPS, often preferred in patients with Parkinson’s disease who develop psychosis. * **Hyperprolactinemia** is also minimal with Clozapine compared to typical antipsychotics and Risperidone.

Question 327: In an acute attack of migraine, what is the drug of choice?

A. Ergotamine tartrate (Correct Answer)
B. Methysergide
C. Propranolol
D. Caffeine

Explanation: **Explanation:** **Correct Option: A. Ergotamine tartrate** Ergotamine is a non-selective 5-HT$_{1}$ receptor agonist (specifically 5-HT$_{1B/1D}$) that causes potent vasoconstriction of dilated cranial blood vessels and inhibits neurogenic inflammation. It is considered a drug of choice for **aborting an acute attack** of moderate-to-severe migraine, especially when triptans are unavailable or ineffective. It is often combined with caffeine to enhance its absorption. **Analysis of Incorrect Options:** * **B. Methysergide:** This is a 5-HT$_2$ antagonist used exclusively for the **prophylaxis** of migraine. It is rarely used today due to the risk of serious side effects like retroperitoneal, pulmonary, and endocardial fibrosis. * **C. Propranolol:** This is a beta-blocker and is the **first-line drug for the prophylaxis** (prevention) of migraine. It has no role in treating an acute attack as it does not provide immediate relief. * **D. Caffeine:** While caffeine is used as an **adjuvant** in acute migraine therapy to increase the gastrointestinal absorption of ergotamine and paracetamol, it is not a primary drug of choice when used alone. **NEET-PG High-Yield Pearls:** * **Drug of Choice (DOC) for Mild-Moderate Acute Attack:** NSAIDs (e.g., Aspirin, Naproxen). * **DOC for Severe Acute Attack:** Triptans (e.g., Sumatriptan). Note: If Triptans are not in options, Ergotamine is the preferred answer. * **DOC for Prophylaxis:** Propranolol. * **Contraindication:** Ergotamine and Triptans are contraindicated in patients with Coronary Artery Disease (CAD) or peripheral vascular disease due to their vasoconstrictive properties. * **Triptan Mechanism:** Selective 5-HT$_{1B/1D}$ agonists.

Question 328: What is the action of flumazenil on the benzodiazepine receptor?

A. Agonist
B. Partial agonist
C. Inverse agonist
D. Antagonist (Correct Answer)

Explanation: **Explanation:** **Mechanism of Action:** Flumazenil is a specific **competitive antagonist** at the benzodiazepine (BZD) binding site on the GABA-A receptor complex. It binds with high affinity but possesses zero intrinsic activity. By occupying the receptor, it prevents benzodiazepines (and "Z-drugs" like Zolpidem) from exerting their effects, effectively reversing sedation and respiratory depression. **Analysis of Options:** * **A. Agonist:** Agonists (e.g., Diazepam) bind to the receptor and increase the frequency of chloride channel opening, leading to CNS depression. * **B. Partial Agonist:** These (e.g., Bretazenil) produce a sub-maximal response compared to full agonists; flumazenil does not activate the receptor at all. * **C. Inverse Agonist:** These (e.g., Beta-carbolines) bind to the BZD site but produce the opposite effect of agonists, causing anxiety and seizures. * **D. Antagonist (Correct):** Flumazenil blocks the site without triggering a biological response, neutralizing both agonists and inverse agonists. **High-Yield Clinical Pearls for NEET-PG:** * **Indications:** Management of BZD overdose and reversal of conscious sedation induced by BZDs during diagnostic procedures. * **Pharmacokinetics:** It has a very **short half-life** (approx. 1 hour). Because many BZDs (like Diazepam) last longer, "re-sedation" can occur, requiring repeated doses or an infusion. * **Contraindication/Risk:** In patients with long-term BZD dependence, flumazenil can precipitate **acute withdrawal symptoms**, most notably **seizures**. It is also contraindicated in tricyclic antidepressant (TCA) overdose due to increased seizure risk. * **Note:** It does **not** reverse the effects of Barbiturates, Alcohol, or General Anesthetics.

Question 329: What is the recommended route of administration for fosphenytoin?

A. Intravenous (Correct Answer)
B. Subcutaneous
C. Oral
D. Intradermal

Explanation: **Explanation:** **Fosphenytoin** is a water-soluble prodrug of phenytoin, specifically designed for parenteral use [1]. The correct answer is **Intravenous (IV)** because fosphenytoin is rapidly converted to phenytoin by phosphatases in the blood and liver. It is the preferred agent for the emergency management of **Status Epilepticus** when intravenous access is available, as it is significantly safer than IV phenytoin [1]. * **Why Intravenous is correct:** Fosphenytoin is highly water-soluble and has a neutral pH (8.6–9.0). Unlike phenytoin, which is highly alkaline and requires propylene glycol as a solvent, fosphenytoin does not cause tissue necrosis or "Purple Glove Syndrome" [1]. It can be infused at a faster rate (up to 150 mg PE/min) than phenytoin [1]. * **Why other options are incorrect:** * **Oral:** Fosphenytoin is not administered orally because it is a prodrug meant to bypass the solubility issues of parenteral phenytoin. For maintenance therapy, standard **Phenytoin** tablets/capsules are used [2]. * **Subcutaneous/Intradermal:** These routes are not used for fosphenytoin as they do not provide the rapid systemic distribution required for seizure control and may cause local irritation. Note: Fosphenytoin *can* be given **Intramuscularly (IM)**, but IV remains the primary recommended route for acute stabilization [2]. **High-Yield Clinical Pearls for NEET-PG:** 1. **Dosing:** Fosphenytoin is prescribed in **Phenytoin Equivalents (PE)**. 1.5 mg of fosphenytoin = 1 mg of phenytoin = 1 mg PE. 2. **Advantage:** It can be mixed with common IV fluids like Normal Saline or Dextrose, whereas phenytoin precipitates in Dextrose [1]. 3. **Side Effects:** While it avoids local skin complications, rapid IV infusion can still cause **cardiac arrhythmias** and hypotension; ECG monitoring is mandatory [1].

Question 330: All of the following act on the GABA receptor except?

A. Propofol
B. Thiopentone
C. Etomidate
D. Dexmedetomidine (Correct Answer)

Explanation: **Explanation:** The correct answer is **Dexmedetomidine** because its mechanism of action is entirely independent of the GABAergic system. **1. Why Dexmedetomidine is the correct answer:** Dexmedetomidine is a highly selective **central alpha-2 ($\alpha_2$) adrenergic agonist**. It acts primarily on the locus coeruleus in the brainstem to induce sedation and analgesia. Unlike most intravenous anesthetics, it produces "conscious sedation" (the patient remains easily arousable) and does not cause significant respiratory depression. **2. Why the other options are incorrect:** * **Propofol:** Acts by facilitating inhibitory neurotransmission through **GABA-A receptors**. It increases the duration of chloride channel opening. * **Thiopentone (Barbiturates):** Acts on the **GABA-A receptor** at a site distinct from benzodiazepines. At low doses, it increases the duration of chloride channel opening; at high doses, it can directly mimic GABA (GABA-mimetic action). * **Etomidate:** A carboxylated imidazole derivative that acts as a potent and selective **GABA-A receptor** modulator, specifically enhancing the effects of GABA. **High-Yield Clinical Pearls for NEET-PG:** * **Dexmedetomidine:** Known for its "analgesic-sparing effect" and is the drug of choice for sedation in the ICU for non-intubated patients. A common side effect is bradycardia. * **Etomidate:** Best for hemodynamically unstable patients (cardiovascular stability) but can cause **adrenocortical suppression** by inhibiting the enzyme 11-beta-hydroxylase. * **Propofol:** Drug of choice for Day Care Surgery due to rapid recovery and anti-emetic properties. * **Ketamine:** Unlike the others, this acts on **NMDA receptors** (antagonist) and is the only induction agent that stimulates the sympathetic nervous system.

Practice by Chapter

General Anesthetics

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Local Anesthetics

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Sedative-Hypnotics

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Antiepileptic Drugs

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Antiparkinsonian Drugs

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Opioid Analgesics

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Drugs of Abuse and Addiction

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Psychostimulants

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Hallucinogens

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CNS Stimulants and Cognitive Enhancers

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