Central Nervous System Pharmacology Practice Questions

Q: Which of the following drugs is least absorbed from the mucous membrane?

Procaine. **Explanation:** The absorption of local anesthetics (LAs) through mucous membranes depends primarily on their **lipid solubility** and **vasoactive properties**. **Why Procaine is the Correct Answer:** Procaine is an ester-linked local anesthetic with **very low lipid solubility**. Because the mucous membrane barrier is lipid-rich, drugs with low lipid solubility penetrate poorly. Furthermore, Procaine is a potent **vasodilator**, which increases its systemic absorption into the bloodstream but prevents it from remaining concentrated at the site of application. Consequently, it has negligible topical (surface) anesthetic activity and is considered the least effective for mucosal application among the options. **Analysis of Incorrect Options:** * **Lidocaine (Option A):** An amide with moderate lipid solubility. It is highly effective and widely used for topical anesthesia (e.g., 2% jelly, 10% spray). * **Tetracaine (Option B):** An ester with high lipid solubility and potency. It is frequently used for surface anesthesia, particularly in ophthalmology and spinal anesthesia. * **Cocaine (Option D):** Unique among LAs because it is a potent **vasoconstrictor**. This property, combined with good lipid solubility, allows it to be rapidly and effectively absorbed through mucous membranes (e.g., nasal mucosa). **NEET-PG High-Yield Pearls:** 1. **Lipid Solubility:** Determines the **potency** and topical effectiveness of a local anesthetic. 2. **pKa:** Determines the **onset of action** (lower pKa = faster onset). 3. **Protein Binding:** Determines the **duration of action**. 4. **Vasoactivity:** Most LAs are vasodilators (except Cocaine, Ropivacaine, and Levobupivacaine). 5. **Metabolism:** Esters (like Procaine) are metabolized by **plasma pseudocholinesterase**; Amides (like Lidocaine) are metabolized by **liver microsomal enzymes**.

Q: What is the action of flumazenil on the benzodiazepine receptor?

Antagonist. **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.

Q: Which of the following local anesthetics is most likely to produce an allergic reaction?

Benzocaine. **Explanation:** The correct answer is **Benzocaine** because it belongs to the **Ester group** of local anesthetics (LAs). 1. **Why Benzocaine is correct:** Local anesthetics are classified into two groups: Esters and Amides. Esters (like Benzocaine, Procaine, and Tetracaine) are derivatives of **para-aminobenzoic acid (PABA)**. PABA is a known potent allergen; therefore, ester-linked LAs are much more likely to cause hypersensitivity reactions. 2. **Why other options are incorrect:** Prilocaine, Ropivacaine, and Etidocaine are all **Amide-linked** local anesthetics. Amides are metabolized in the liver and do not produce PABA. True allergic reactions to amides are extremely rare; most adverse reactions reported with amides are actually due to systemic toxicity (LAST) or preservatives like methylparaben. **High-Yield NEET-PG Pearls:** * **The "i" Rule:** To distinguish between the two classes, remember that **Amides** have two "i"s in their name (L**i**doca**i**ne, Pr**i**loca**i**ne, Bup**i**vaca**i**ne, Rop**i**vaca**i**ne), while **Esters** have only one "i" (Benzoca**i**ne, Coca**i**ne, Proca**i**ne). * **Benzocaine Clinical Note:** It is commonly used as a topical spray. Apart from allergy, it is high-yield for causing **Methemoglobinemia** (treated with Methylene blue). * **Cross-reactivity:** There is cross-reactivity among esters, but no cross-reactivity between esters and amides. If a patient is allergic to an ester, an amide is a safe alternative.

Q: Which of the following congenital anomalies is seen with maternal use of cocaine?

Cleft palate. **Explanation:** The correct answer is **C. Cleft palate.** **Mechanism of Action:** Cocaine is a potent sympathomimetic agent that acts as a powerful **vasoconstrictor**. It inhibits the reuptake of norepinephrine and dopamine at the presynaptic nerve terminals. In pregnancy, cocaine crosses the placenta and causes acute maternal and fetal hypertension and tachycardia. The primary mechanism for congenital anomalies is **vascular disruption**. Severe vasoconstriction leads to localized ischemia in developing fetal tissues, resulting in structural defects such as **cleft lip/palate**, segmental intestinal atresia, and limb reduction defects. **Analysis of Incorrect Options:** * **A. Sacral agenesis:** This is the most specific (pathognomonic) anomaly associated with **Maternal Diabetes Mellitus**, not cocaine use. * **B. Hydrops:** While cocaine can cause placental abruption or fetal growth restriction (FGR), it is not a classic cause of non-immune hydrops fetalis. Hydrops is more commonly associated with Rh isoimmunization, Parvovirus B19, or chromosomal anomalies. * **D. Hypertrichosis:** This (specifically synophrys/thick eyebrows) is a feature of **Fetal Alcohol Syndrome (FAS)** or certain genetic syndromes (e.g., Cornelia de Lange), but not cocaine exposure. **High-Yield Clinical Pearls for NEET-PG:** * **Most common complication:** Cocaine is most strongly associated with **Placental Abruption** (due to acute hypertension) and **IUGR/Fetal Growth Restriction**. * **Vascular Disruption Sequence:** Cocaine is linked to **Gastroschisis** and **Urinary tract anomalies** (e.g., prune belly syndrome) via the same ischemic mechanism. * **Neurobehavioral effects:** Neonates may present with irritability, tremors, and abnormal sleep patterns (often termed "Cocaine babies").

Q: What is the recommended route of administration for fosphenytoin?

Intravenous. **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].

Q: All of the following act on the GABA receptor except?

Dexmedetomidine. **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.

Q: Which of the following is a vasoconstrictor?

None of the above. **Explanation:** The fundamental pharmacological property of almost all local anesthetics (LAs) is **vasodilation**. They achieve this by relaxing the vascular smooth muscle. This vasodilation increases the rate of systemic absorption, shortens the duration of the block, and increases the risk of systemic toxicity. **Why "None of the above" is correct:** Options A, B, and C (Bupivacaine, Procaine, and Lidocaine) are all potent vasodilators. Therefore, none of them act as vasoconstrictors. In clinical practice, a vasoconstrictor like **Adrenaline (Epinephrine)** is often added to these drugs to counteract their vasodilatory effects, thereby prolonging the duration of action and reducing surgical bleeding. **Analysis of Options:** * **Bupivacaine:** A long-acting amide LA. It is a potent vasodilator and is notably the most cardiotoxic LA. * **Procaine:** An ester-linked LA. It is a very strong vasodilator with a short duration of action. * **Lidocaine:** The most commonly used amide LA. It causes significant vasodilation, which is why it is frequently formulated with adrenaline (1:200,000). **High-Yield NEET-PG Pearls:** 1. **The Exceptions:** **Cocaine** is the only naturally occurring LA that is a potent **vasoconstrictor** (it inhibits norepinephrine reuptake). 2. **Modern Exceptions:** Among synthetic LAs, **Ropivacaine** and **Levobupivacaine** possess mild intrinsic vasoconstrictive properties at lower concentrations. 3. **Adrenaline Addition:** Adding adrenaline to LAs is contraindicated in "end-artery" areas (fingers, toes, penis, nose, and earlobes) due to the risk of ischemic necrosis. 4. **Prilocaine:** Another amide LA that has minimal vasodilatory effects compared to lidocaine.

Question 1

What is produced by the supersensitivity of Dopamine receptors?

Accepted Answer

Dyskinesia

Answer

Hyperphagia

Answer

Hyperpathia

Answer

Hypomania

Question 2

Which of the following drugs is least absorbed from the mucous membrane?

Accepted Answer

Procaine

Answer

Lidocaine

Answer

Tetracaine

Answer

Cocaine

Question 3

What is the action of flumazenil on the benzodiazepine receptor?

Accepted Answer

Antagonist

Answer

Agonist

Answer

Partial agonist

Answer

Inverse agonist

Question 4

Which of the following local anesthetics is most likely to produce an allergic reaction?

Accepted Answer

Benzocaine

Answer

Prilocaine

Answer

Ropivacaine

Answer

Etidocaine

Question 5

Which of the following congenital anomalies is seen with maternal use of cocaine?

Accepted Answer

Cleft palate

Answer

Sacral agenesis

Answer

Hydrops

Answer

Hypertrichosis

Question 6

What is the recommended route of administration for fosphenytoin?

Accepted Answer

Intravenous

Answer

Subcutaneous

Answer

Oral

Answer

Intradermal

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

All of the following act on the GABA receptor except?

Accepted Answer

Dexmedetomidine

Answer

Propofol

Answer

Thiopentone

Answer

Etomidate

Question 9

Regarding phenytoin, all are true except?

Accepted Answer

At lower concentrations, it follows zero-order kinetics

Answer

Potent microsomal enzyme inducer

Answer

Highly protein bound

Answer

With increasing dose, the Vmax increases.

Question 10

Which of the following is a vasoconstrictor?

Accepted Answer

None of the above

Answer

Bupivacaine

Answer

Procaine

Answer

Lidocaine

Central Nervous System Pharmacology — MCQs

Central Nervous System Pharmacology — MCQs

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