Central Nervous System Pharmacology — MCQs

Central Nervous System Pharmacology Indian Medical PG Practice Questions and MCQs

Question 651: All the following statements regarding remifentanil are true EXCEPT?

A. Useful for short painful procedures
B. Metabolized by plasma esterases
C. Equipotent as fentanyl
D. Long acting anesthetic (Correct Answer)

Explanation: Remifentanil is a unique, ultra-short-acting synthetic opioid analgesic used primarily in anesthesia. The correct answer is **D (Long acting anesthetic)** because remifentanil is characterized by its exceptionally short duration of action, not a long one [1]. **1. Why Option D is the correct answer (The Exception):** Remifentanil has a unique chemical structure containing an ester linkage. This allows it to undergo rapid hydrolysis by **non-specific tissue and plasma esterases**. Consequently, it has an ultra-short half-life (approximately 3–10 minutes) and a context-sensitive half-time that remains constant regardless of the duration of infusion [1]. This makes it the shortest-acting opioid available. **2. Analysis of Incorrect Options:** * **Option A (Useful for short painful procedures):** Due to its rapid onset and offset, it is ideal for procedures requiring intense analgesia for a brief period (e.g., intubation, brief surgeries) without prolonged respiratory depression. * **Option B (Metabolized by plasma esterases):** This is its defining pharmacokinetic feature. Unlike other opioids metabolized by the liver (CYP450), remifentanil metabolism is independent of hepatic or renal function. * **Option C (Equipotent as fentanyl):** Remifentanil and fentanyl are considered roughly equipotent in terms of analgesic strength, though remifentanil acts much faster and wears off sooner. **Clinical Pearls for NEET-PG:** * **Context-Sensitive Half-Time:** Remifentanil is the only opioid where this remains nearly constant (~3 mins) even after a 10-hour infusion. * **Organ-Independent Elimination:** It is the drug of choice for patients with end-stage liver or renal failure. * **Opioid-Induced Hyperalgesia:** Rapid withdrawal or high doses of remifentanil can sometimes lead to acute postoperative hyperalgesia. * **Mnemonic:** **R**emifentanil = **R**apidly metabolized by **R**BC/Plasma esterases.

Question 652: All of the following can be used to treat alcohol dependence except?

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

Explanation: **Explanation:** The goal of treating alcohol dependence is to maintain abstinence and prevent relapse. **Flumazenil (Option C)** is the correct answer because it is a competitive **GABA-A receptor antagonist** used specifically for the reversal of **Benzodiazepine overdose**. It has no established role in the long-term management of alcohol dependence. **Analysis of Options:** * **Naltrexone (Option A):** An opioid receptor antagonist that reduces the "reward" or euphoria associated with drinking by blocking endogenous opioid release. It is effective in reducing cravings and the frequency of heavy drinking. * **Acamprosate (Option B):** A NMDA receptor antagonist and GABA-A enhancer. It helps maintain abstinence by restoring the chemical balance in the brain (homeostasis) that is disrupted by chronic alcohol use. It is particularly useful 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 (aversion therapy). **NEET-PG High-Yield Pearls:** * **First-line drugs** for alcohol dependence: Naltrexone and Acamprosate. * **Disulfiram** is considered second-line due to compliance issues and safety profiles. * **Topiramate** and **Baclofen** are off-label options often tested as "newer agents" for alcohol dependence. * **Wernicke’s Encephalopathy:** Always give Thiamine (B1) *before* Glucose in alcoholic patients to prevent precipitating acute neurological symptoms.

Question 653: No treatment of withdrawal is required in which of the following?

A. LSD (Correct Answer)
B. Opium
C. Alcohol
D. Amphetamine

Explanation: **Explanation:** The correct answer is **LSD (Lysergic Acid Diethylamide)**. **1. Why LSD is correct:** LSD is a potent hallucinogen that acts primarily as a partial agonist at 5-HT2A receptors. Unlike opioids or alcohol, LSD does not lead to significant physical dependence or a predictable physiological withdrawal syndrome upon discontinuation. While users may experience psychological effects or "flashbacks" (Hallucinogen Persisting Perception Disorder), there are no life-threatening or medically significant physical withdrawal symptoms that require pharmacological intervention. **2. Why the other options are incorrect:** * **Opium (Opioids):** Withdrawal is characterized by intense physical symptoms including lacrimation, rhinorrhea, yawning, sweating, and painful muscle cramps. While rarely fatal, it is highly distressing and often requires treatment with Methadone or Buprenorphine. * **Alcohol:** Withdrawal can be life-threatening. It ranges from mild tremors to **Delirium Tremens (DTs)** and seizures. Management with Benzodiazepines (e.g., Diazepam, Chlordiazepoxide) is mandatory to prevent mortality. * **Amphetamine:** Withdrawal leads to a "crash" characterized by profound depression, fatigue, hypersomnia, and increased appetite. While not usually fatal, supportive care and sometimes antidepressants are required due to the high risk of suicidal ideation. **Clinical Pearls for NEET-PG:** * **Tolerance vs. Dependence:** LSD shows rapid **tachyphylaxis** (rapidly developing tolerance), but it does not activate the dopaminergic reward pathway in the nucleus accumbens, which explains the lack of physical addiction. * **Flashbacks:** Also known as Hallucinogen Persisting Perception Disorder (HPPD), these are unique to hallucinogens and occur long after the drug has cleared the system. * **Antidote for "Bad Trip":** If a patient presents with acute LSD agitation, the treatment of choice is **Benzodiazepines** or supportive reassurance ("talking down").

Question 654: Sumatriptan exerts antimigraine action through which receptors?

A. 5HT1D/1B (Correct Answer)
B. 5HT2
C. 5HT3
D. 5HT4

Explanation: **Explanation:** **Sumatriptan** is the prototype of the "Triptan" class, which are first-line drugs for the treatment of acute migraine attacks. Its antimigraine action is mediated primarily through selective agonism at **5-HT1B and 5-HT1D receptors**. 1. **Why Option A is correct:** * **5-HT1B receptors** are located on the smooth muscles of cranial blood vessels. Activation causes **vasoconstriction** of the pathologically dilated intracranial extracerebral vessels. * **5-HT1D receptors** are presynaptic autoreceptors on trigeminal nerve endings. Activation **inhibits the release of pro-inflammatory neuropeptides** (like CGRP and Substance P), thereby suppressing "neurogenic inflammation." 2. **Why other options are incorrect:** * **5-HT2:** These receptors (specifically 5-HT2A/2C) are involved in platelet aggregation and smooth muscle contraction. Antagonists like Methysergide were historically used for migraine *prophylaxis*, not acute treatment. * **5-HT3:** These are ionotropic receptors located in the Chemoreceptor Trigger Zone (CTZ). Antagonists (e.g., Ondansetron) are used as anti-emetics. * **5-HT4:** These receptors are primarily involved in gastrointestinal motility. Agonists (e.g., Prucalopride) are used as prokinetics. **High-Yield Clinical Pearls for NEET-PG:** * **Route of Administration:** Sumatriptan has low oral bioavailability (~15%); the subcutaneous route is the fastest and most effective for severe attacks. * **Contraindications:** Due to its vasoconstrictive properties, it is strictly contraindicated in patients with **Ischemic Heart Disease (IHD)**, Prinzmetal angina, and uncontrolled hypertension. * **Adverse Effects:** "Triptan sensations" (tightness/pressure in the chest and throat) and tingling/warmth. * **Drug Interaction:** Do not co-administer with MAO inhibitors or within 24 hours of Ergotamine.

Question 655: All of the following benzodiazepines can be used in the elderly and those with liver disease EXCEPT?

A. Lorazepam
B. Oxazepam
C. Triazolam
D. Diazepam (Correct Answer)

Explanation: **Explanation:** The primary concern when prescribing benzodiazepines (BZDs) to elderly patients or those with hepatic impairment is the risk of drug accumulation and prolonged sedation. Most BZDs undergo **Phase I metabolism** (oxidation) via the Cytochrome P450 system before entering **Phase II metabolism** (glucuronidation). **Why Diazepam is the Correct Answer:** Diazepam is a long-acting BZD that undergoes extensive Phase I metabolism in the liver. It produces multiple active metabolites, such as **desmethyldiazepam**, which has an extremely long half-life (up to 100 hours). In elderly patients or those with liver disease, Phase I oxidative reactions are significantly impaired, leading to the accumulation of these active metabolites. This increases the risk of "cumulative toxicity," manifesting as over-sedation, cognitive impairment, and an increased risk of falls/fractures. **Why the other options are incorrect:** * **Lorazepam (A) and Oxazepam (B):** These drugs belong to the **"LOT"** group (Lorazepam, Oxazepam, Temazepam). They bypass Phase I oxidation and are directly metabolized via **Phase II glucuronidation**. Since glucuronidation is relatively preserved in the elderly and in patients with liver cirrhosis, these drugs are considered safer. * **Triazolam (C):** While it undergoes Phase I metabolism, it is an ultra-short-acting BZD with no active metabolites. Its rapid clearance makes it less likely to cause cumulative toxicity compared to Diazepam. **NEET-PG High-Yield Pearls:** * **Mnemonic "LOT":** **L**orazepam, **O**xazepam, and **T**emazepam are the BZDs of choice for patients with liver failure or the elderly. * **Diazepam** is also avoided in the elderly due to its high lipid solubility, which increases its volume of distribution in aged bodies with higher fat content. * **Drug of choice for Status Epilepticus:** Lorazepam (IV). * **Drug of choice for Alcohol Withdrawal:** Chlordiazepoxide (or Lorazepam if liver enzymes are elevated).

Question 656: Which of the following inducing agents produces cardiac stability?

A. Etomidate (Correct Answer)
B. Ketamine
C. Halothane
D. Thiopentone

Explanation: **Explanation:** **Etomidate** is the induction agent of choice for patients with compromised cardiovascular status (e.g., coronary artery disease, valvular heart disease, or hypovolemia) because it provides the greatest **hemodynamic stability**. Unlike other induction agents, it has minimal to no effect on heart rate, myocardial contractility, or systemic vascular resistance. It achieves this by having negligible effects on the sympathetic nervous system and baroreceptor reflexes. **Analysis of Incorrect Options:** * **Ketamine:** While it often maintains blood pressure, it does so by **stimulating** the sympathetic nervous system (increasing HR and BP). This increases myocardial oxygen demand, making it potentially dangerous in patients with ischemic heart disease. * **Halothane:** This is an inhalational anesthetic known for **sensitizing the myocardium to catecholamines**, which can lead to arrhythmias. It also causes significant myocardial depression and hypotension. * **Thiopentone:** A potent venodilator and myocardial depressant. It causes a significant drop in blood pressure and is contraindicated in patients with shock or severe hypovolemia. **High-Yield Clinical Pearls for NEET-PG:** * **The "Trade-off":** While Etomidate is cardio-stable, its major drawback is **adrenocortical suppression** (inhibits 11-beta-hydroxylase), making it risky for prolonged infusions or septic patients. * **Myoclonus:** Etomidate is frequently associated with involuntary muscle movements during induction. * **Drug of Choice for ECT:** Methohexital is preferred, but Etomidate is an alternative as it does not significantly shorten seizure duration. * **Propofol vs. Etomidate:** Propofol is the most common induction agent but causes significant hypotension; Etomidate is reserved for the "hemodynamically unstable" patient.

Question 657: Naltrexone is used to maintain abstinence following opioid withdrawal in addicts. It blocks which of the following features of opioid use, except?

A. Euphoriant effects of opioids
B. Craving for opioids (Correct Answer)
C. Miosis
D. Respiratory depression

Explanation: **Explanation:** Naltrexone is a long-acting, competitive **opioid receptor antagonist** with high affinity for $\mu$ (mu) receptors. Its primary mechanism is to occupy opioid receptors, thereby preventing exogenous opioids from binding and exerting their pharmacological effects. **Why "Craving for opioids" is the correct answer:** While Naltrexone is used to maintain abstinence, it primarily works by blocking the **reinforcing effects** (the "high") of opioids. Unlike Methadone or Buprenorphine (which are agonists/partial agonists), Naltrexone does not satisfy the pharmacological craving for opioids. In fact, poor compliance is common because it does not reduce the psychological drive or "hunger" for the drug as effectively as substitution therapy does. Note: While Naltrexone is FDA-approved for alcohol craving, its role in reducing *opioid* craving is clinically considered minimal compared to its blockade of physical effects. **Analysis of Incorrect Options:** * **A. Euphoriant effects:** By blocking $\mu$-receptors in the reward pathway (nucleus accumbens), Naltrexone completely abolishes the "rush" or euphoria associated with opioid use. * **C & D. Miosis and Respiratory depression:** These are classical pharmacological actions mediated by $\mu$ and $\kappa$ receptors. As a competitive antagonist, Naltrexone blocks all acute physiological effects of opioids, including pupillary constriction and life-threatening respiratory depression. **High-Yield Clinical Pearls for NEET-PG:** * **Administration:** Naltrexone is orally active with a long half-life (up to 10 hours; its metabolite 6-$\beta$-naltrexol lasts even longer). * **Prerequisite:** It must **never** be started until a patient is opioid-free for at least 7–10 days. Administering it earlier will precipitate **severe acute withdrawal syndrome**. * **Alcoholism:** It is also a first-line treatment for alcohol dependence, where it reduces the "reward" of drinking by blocking endogenous opioid release. * **Naloxone vs. Naltrexone:** Remember **Naloxone** is for acute toxicity (IV, short-acting), while **Naltrexone** is for maintenance/relapse prevention (Oral, long-acting).

Question 658: Naltrexone is used to maintain abstinence following opioid withdrawal in addicts. It blocks which of the following features of opioid use, except?

A. Euphoriant effects of opioids
B. Craving for opioids (Correct Answer)
C. Miosis
D. Respiratory depression

Explanation: **Explanation:** Naltrexone is a long-acting, orally effective **competitive opioid antagonist** with a high affinity for $\mu$ (mu) receptors. Understanding its mechanism is key to solving this question. **Why "Craving for opioids" is the correct answer:** Naltrexone works by blocking the pharmacological effects of exogenous opioids. If a patient on Naltrexone takes an opioid, they will not experience the "high" because the receptors are occupied. However, Naltrexone **does not significantly reduce the psychological craving** for opioids in the same way that agonists (like Methadone) or partial agonists (like Buprenorphine) do. While it is used to maintain abstinence, its primary role is to prevent relapse by neutralizing the reinforcing effects of the drug, rather than eliminating the desire to use it. **Analysis of incorrect options:** * **A. Euphoriant effects:** Naltrexone competitively blocks $\mu$-receptors in the reward pathway, effectively preventing the euphoria (the "rush") associated with opioid use. * **C & D. Miosis and Respiratory depression:** These are classic pharmacological actions of opioids mediated by $\mu$ and $\kappa$ receptors. As a competitive antagonist, Naltrexone blocks all acute physiological effects of opioids, including pupillary constriction and life-threatening respiratory depression. **High-Yield Clinical Pearls for NEET-PG:** * **Naltrexone vs. Naloxone:** Naloxone is short-acting and given parenterally (used for acute toxicity); Naltrexone is long-acting and given orally (used for maintenance). * **Alcoholism:** Naltrexone is also FDA-approved for **Alcohol Dependence** because it blocks the endogenous opioid-mediated reinforcement of alcohol consumption. * **Prerequisite:** Never start Naltrexone until the patient is opioid-free for at least **7–10 days** to avoid precipitating severe withdrawal symptoms. * **Vivitrol:** This is the extended-release injectable form of Naltrexone used to improve compliance.

Question 659: Which of the following is NOT an adverse effect of Selective Serotonin Reuptake Inhibitors (SSRIs)?

A. Weight changes
B. Diarrhoea
C. Delayed ejaculation
D. Galactorrhea (Correct Answer)

Explanation: **Explanation:** The correct answer is **D. Galactorrhea**. **1. Why Galactorrhea is the correct choice:** Galactorrhea (inappropriate milk production) is primarily caused by **hyperprolactinemia**. Prolactin secretion is inhibited by **Dopamine** (acting as Prolactin Inhibiting Factor). Drugs that block D2 receptors (like typical antipsychotics) or deplete dopamine (like Reserpine) lead to increased prolactin levels. **SSRIs primarily affect the serotonergic system**, not the dopaminergic pathway, and therefore do not typically cause galactorrhea. **2. Analysis of Incorrect Options:** * **A. Weight changes:** SSRIs can cause initial weight loss, but long-term use (especially with Paroxetine) is frequently associated with **weight gain**. * **B. Diarrhoea:** Serotonin (5-HT) is abundant in the GI tract. By increasing synaptic 5-HT, SSRIs stimulate 5-HT3 and 5-HT4 receptors, leading to nausea, vomiting, and **diarrhoea** (the most common acute side effects). * **C. Delayed ejaculation:** Sexual dysfunction is the most common long-term side effect of SSRIs. It includes decreased libido and **delayed ejaculation/anorgasmia**. This property is actually utilized therapeutically in treating premature ejaculation (e.g., Dapoxetine). **3. NEET-PG High-Yield Pearls:** * **Drug of Choice:** SSRIs are the first-line treatment for Depression, OCD, Panic Disorder, Social Phobia, and PTSD. * **Fluoxetine:** Has the longest half-life (due to its active metabolite norfluoxetine); least likely to cause withdrawal symptoms. * **Serotonin Syndrome:** A dangerous interaction when SSRIs are combined with MAO inhibitors, characterized by hyperthermia, muscle rigidity, and cardiovascular collapse. * **Discontinuation Syndrome:** Characterized by "FINISH" symptoms (Flu-like symptoms, Insomnia, Nausea, Imbalance, Sensory disturbances, Hyperarousal).

Question 660: Ethanol is administered in methyl alcohol poisoning because it:

A. Inhibits alcohol dehydrogenase (Correct Answer)
B. Inhibits aldehyde synthetase
C. Binds 100 times stronger than methanol
D. None of the above

Explanation: **Explanation:** The toxicity of **Methyl alcohol (Methanol)** is not due to the alcohol itself, but its metabolites. Methanol is metabolized by the enzyme **Alcohol Dehydrogenase (ADH)** into **Formaldehyde**, which is then converted by aldehyde dehydrogenase into **Formic acid**. Formic acid is highly toxic, leading to metabolic acidosis and retinal damage (blindness). **Why Option A is Correct:** Ethanol acts as a **competitive inhibitor** of Alcohol Dehydrogenase. It has a much higher affinity (approx. 20 times) for ADH than methanol. By saturating the enzyme, ethanol prevents the conversion of methanol into its toxic metabolites. This allows the unchanged methanol to be excreted harmlessly through the lungs and kidneys. **Why Other Options are Incorrect:** * **Option B:** "Aldehyde synthetase" is not the target enzyme in this pathway. The relevant enzymes are Alcohol Dehydrogenase and Aldehyde Dehydrogenase. * **Option C:** While ethanol has a higher affinity for ADH, the "100 times stronger" figure is inaccurate. It is generally cited as having **20 times** higher affinity. **High-Yield Clinical Pearls for NEET-PG:** 1. **Fomepizole:** This is the preferred specific antidote for methanol and ethylene glycol poisoning. It is a potent inhibitor of ADH and is preferred over ethanol because it does not cause CNS depression or hypoglycemia. 2. **Folate Therapy:** Leucovorin (folinic acid) is administered to enhance the breakdown of formic acid into $CO_2$ and water. 3. **Dialysis:** Hemodialysis is indicated if methanol levels are >50 mg/dL or if there is severe metabolic acidosis/visual impairment. 4. **Classic Presentation:** "Snowstorm vision" or blurred vision with a high anion gap metabolic acidosis.

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