Central Nervous System Pharmacology Practice Questions

Q: All the following statements regarding remifentanil are true EXCEPT?

Long acting anesthetic. 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.

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

Flumazenil. **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.

Q: Sumatriptan exerts antimigraine action through which receptors?

5HT1D/1B. **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.

Q: Which of the following inducing agents produces cardiac stability?

Etomidate. **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.

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

Galactorrhea. **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).

Q: Ethanol is administered in methyl alcohol poisoning because it:

Inhibits alcohol dehydrogenase. **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.

Question 1

All the following statements regarding remifentanil are true EXCEPT?

Accepted Answer

Long acting anesthetic

Answer

Useful for short painful procedures

Answer

Metabolized by plasma esterases

Answer

Equipotent as fentanyl

Question 2

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

Accepted Answer

Flumazenil

Answer

Naltrexone

Answer

Acamprosate

Answer

Disulfiram

Question 3

No treatment of withdrawal is required in which of the following?

Accepted Answer

LSD

Answer

Opium

Answer

Alcohol

Answer

Amphetamine

Question 4

Sumatriptan exerts antimigraine action through which receptors?

Accepted Answer

5HT1D/1B

Answer

5HT2

Answer

5HT3

Answer

5HT4

Question 5

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

Accepted Answer

Diazepam

Answer

Lorazepam

Answer

Oxazepam

Answer

Triazolam

Question 6

Which of the following inducing agents produces cardiac stability?

Accepted Answer

Etomidate

Answer

Ketamine

Answer

Halothane

Answer

Thiopentone

Question 7

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

Accepted Answer

Craving for opioids

Answer

Euphoriant effects of opioids

Answer

Miosis

Answer

Respiratory depression

Question 8

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

Accepted Answer

Craving for opioids

Answer

Euphoriant effects of opioids

Answer

Miosis

Answer

Respiratory depression

Question 9

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

Accepted Answer

Galactorrhea

Answer

Weight changes

Answer

Diarrhoea

Answer

Delayed ejaculation

Question 10

Ethanol is administered in methyl alcohol poisoning because it:

Accepted Answer

Inhibits alcohol dehydrogenase

Answer

Inhibits aldehyde synthetase

Answer

Binds 100 times stronger than methanol

Answer

None of the above

Central Nervous System Pharmacology — MCQs

Central Nervous System Pharmacology — MCQs

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