Central Nervous System Pharmacology Practice Questions

Q: Which of the following effects is specifically observed with intravenous diazepam and not with other routes of administration?

Coronary dilatation. **Explanation:** The correct answer is **Coronary dilatation**. **Why it is correct:** Intravenous (IV) diazepam is formulated in a solvent called **propylene glycol** because diazepam is poorly soluble in water. When administered intravenously, this solvent—rather than the diazepam molecule itself—exerts a direct vasodilatory effect on the coronary arteries. This specific hemodynamic effect is unique to the IV route and is not observed when the drug is administered orally or intramuscularly. **Analysis of incorrect options:** * **A. Analgesia:** Benzodiazepines (BZDs) like diazepam do not possess analgesic properties. They are used for sedation, anxiolysis, and muscle relaxation, but they do not act on opioid receptors or inhibit pain pathways. * **B. Sedation:** Sedation is the primary pharmacological effect of diazepam regardless of the route (Oral, IV, or Rectal). It is not specific to the intravenous route. * **C. Hypotension:** While rapid IV injection of diazepam can cause a transient drop in blood pressure due to peripheral vasodilation (also partly due to propylene glycol), it is less characteristic and less specific than the coronary dilatation effect often highlighted in pharmacological literature. **High-Yield Clinical Pearls for NEET-PG:** * **Propylene Glycol Toxicity:** High doses of IV diazepam or lorazepam can lead to propylene glycol toxicity, manifesting as anion gap metabolic acidosis and acute kidney injury. * **Injection Site:** IV diazepam is notorious for causing **thrombophlebitis** (painful inflammation of the vein) due to the propylene glycol solvent. * **Drug of Choice:** While diazepam was historically the drug of choice for **Status Epilepticus**, current protocols often prefer **Lorazepam** (IV) due to its longer duration of action in the brain. * **Antidote:** The specific antagonist for benzodiazepine overdose is **Flumazenil**.

Q: Which of the following drugs is not metabolized by the liver?

Oxazepam. **Explanation:** The metabolism of Benzodiazepines (BZDs) primarily occurs via two phases in the liver: **Phase I (Oxidation)** by Cytochrome P450 enzymes and **Phase II (Conjugation)** with glucuronic acid. **Why Oxazepam is the correct answer:** Most BZDs undergo Phase I oxidation to form active metabolites, which significantly prolongs their duration of action. However, a specific group of BZDs—**Oxazepam, Temazepam, and Lorazepam (mnemonic: OTL)**—bypass Phase I oxidation entirely. They undergo direct **Phase II glucuronidation** to form inactive, water-soluble metabolites that are excreted by the kidneys. Because they do not rely on the CYP450 system, they are the drugs of choice in patients with **liver failure** or the **elderly**, where oxidative capacity is diminished. **Analysis of Incorrect Options:** * **Diazepam:** A long-acting BZD that undergoes extensive Phase I metabolism to form active metabolites like desmethyldiazepam (nordiazepam), giving it a very long half-life. * **Flunitrazepam & Nitrazepam:** These are nitro-benzodiazepines. They undergo Phase I reduction and acetylation in the liver before excretion. **NEET-PG High-Yield Pearls:** 1. **OTL (Oxazepam, Temazepam, Lorazepam):** "Outside The Liver" (mnemonic for bypassing Phase I). Safe in cirrhosis and elderly patients. 2. **Active Metabolites:** Diazepam and Chlordiazepoxide have the longest-acting active metabolites. 3. **Enzyme Inhibition:** Drugs like Cimetidine or Erythromycin inhibit CYP450 and can increase the toxicity of Diazepam, but they do **not** affect the clearance of Oxazepam or Lorazepam.

Q: Which of the following does NOT affect the duration of action of local anesthesia?

Non-nervous tissue diffusibility. The duration of action of a local anesthetic (LA) is primarily determined by how long the drug remains in contact with the nerve membrane. This is governed by its chemical properties and local blood flow. ### **Why "Non-nervous tissue diffusibility" is the Correct Answer** Non-nervous tissue diffusibility (or the **pKa/Ionization constant**) primarily determines the **onset of action**, not the duration. A drug’s ability to diffuse through non-neural tissues relates to how quickly it reaches the target nerve. Once the drug is at the nerve, its persistence there (duration) depends on binding and vascular removal, not initial tissue diffusion. ### **Analysis of Incorrect Options** * **Protein Binding (Option A):** This is the **most important** determinant of duration. LAs bind to proteins (like albumin and alpha-1 acid glycoprotein) in the sodium channel. High protein binding (e.g., Bupivacaine, Ropivacaine) results in a longer duration of action compared to low protein binding (e.g., Lidocaine). * **Addition of a Vasoconstrictor (Option B):** Adding Epinephrine causes local vasoconstriction, which decreases the rate of systemic absorption (washout). This keeps the LA at the nerve site longer, thereby increasing the duration. * **Vasodilator Activity (Option C):** Most LAs (except Cocaine and Ropivacaine) are intrinsic vasodilators. Higher intrinsic vasodilatory activity increases blood flow, leading to faster systemic absorption and a **shorter** duration of action. ### **High-Yield NEET-PG Pearls** * **Potency** is determined by **Lipid Solubility**. * **Onset of Action** is determined by **pKa** (Lower pKa = more non-ionized drug = faster onset). * **Duration of Action** is determined by **Protein Binding**. * **Bupivacaine** has the highest protein binding (~95%) and thus a very long duration. * **Cocaine** is the only LA that causes significant vasoconstriction.

Q: Which serotonin-norepinephrine reuptake inhibitor is predominantly used in the condition shown above?

Duloxetine. ***Duloxetine*** - **FDA-approved** specifically for **fibromyalgia** treatment, making it the preferred SNRI for this condition with proven efficacy in clinical trials. - Works by inhibiting both **serotonin and norepinephrine reuptake**, providing dual mechanism for **pain relief** and **mood stabilization** in fibromyalgia patients. *Venlafaxine* - While it is an **SNRI**, it is **not specifically FDA-approved** for fibromyalgia treatment, unlike duloxetine. - Primarily indicated for **depression** and **anxiety disorders**, with less established evidence for fibromyalgia pain management. *Citalopram* - This is a **selective serotonin reuptake inhibitor (SSRI)**, not an SNRI, making it the wrong drug category. - Lacks the **norepinephrine reuptake inhibition** component that is beneficial for **neuropathic pain** management in fibromyalgia. *Escitalopram* - Also an **SSRI**, not an SNRI, so it doesn't fit the question's requirement for a serotonin-norepinephrine reuptake inhibitor. - Primarily used for **depression** and **anxiety disorders** without specific indication for fibromyalgia pain relief.

Q: Which of the following is a long-acting full agonist oral opiate used for heroin detoxification or long-term maintenance?

Methadone. **Explanation:** **Methadone** is the gold standard for the pharmacological management of opioid use disorder (heroin detoxification and maintenance). Its efficacy lies in its unique pharmacokinetic profile: it is a **synthetic full μ-opioid receptor agonist** with high oral bioavailability and an exceptionally **long half-life (24–52 hours)**. In detoxification, methadone prevents withdrawal symptoms by maintaining stable plasma levels, avoiding the "highs and lows" associated with shorter-acting opioids. In long-term maintenance, it induces cross-tolerance, which "blocks" the euphoric effects of illicit heroin if the patient relapses. **Analysis of Incorrect Options:** * **Morphine:** While a full agonist, it has a relatively short half-life (2–4 hours) and significant first-pass metabolism, making it unsuitable for stable long-term maintenance or preventing withdrawal over a 24-hour period. * **Fentanyl:** It is a highly potent, short-acting synthetic opioid. Due to its rapid onset and short duration of action, it is used for anesthesia and acute pain management, but it would worsen addiction cycles if used for detoxification. **High-Yield NEET-PG Pearls:** * **Mechanism:** Apart from being a μ-agonist, Methadone also acts as an **NMDA receptor antagonist**, which may help in reducing opioid tolerance and managing neuropathic pain. * **Side Effects:** A critical ECG finding associated with Methadone is **QTc interval prolongation**, which can lead to Torsades de Pointes. * **Metabolism:** It is primarily metabolized by **CYP3A4**; inhibitors of this enzyme can increase methadone levels, risking respiratory depression. * **Alternative:** **Buprenorphine** (a partial agonist) is also used for maintenance but has a "ceiling effect" on respiratory depression, making it safer in overdose.

Q: What is the mechanism of action of Tolcapone?

COMT inhibitor. **Explanation:** **Mechanism of Action:** Tolcapone is a potent, reversible inhibitor of the enzyme **Catechol-O-methyltransferase (COMT)**. In the management of Parkinson’s disease, when Levodopa is administered, it is peripheralized by COMT into 3-O-methyldopa. Tolcapone inhibits this process, thereby increasing the bioavailability of Levodopa and extending its half-life. Unlike Entacapone (which acts only peripherally), **Tolcapone acts both peripherally and centrally**, crossing the blood-brain barrier to inhibit central COMT. **Analysis of Incorrect Options:** * **Option A (Dopa decarboxylase inhibitor):** This describes **Carbidopa** and **Benserazide**. These drugs prevent the peripheral conversion of Levodopa to Dopamine but do not affect the COMT pathway. * **Option C (MAO-A inhibitor):** These (e.g., **Moclobemide**) are primarily used as antidepressants. Inhibiting MAO-A in the presence of tyramine-rich foods can lead to a "cheese reaction." * **Option D (MAO-B inhibitor):** This describes **Selegiline** and **Rasagiline**. While these are used in Parkinson’s, they work by inhibiting the central breakdown of dopamine rather than the COMT-mediated metabolism of Levodopa. **High-Yield Clinical Pearls for NEET-PG:** * **The "Wearing-Off" Effect:** COMT inhibitors are specifically used to reduce "off" time in patients experiencing fluctuations in Levodopa response. * **Hepatotoxicity:** Tolcapone is associated with a risk of **fulminant hepatic failure**. Therefore, it requires regular liver function test (LFT) monitoring and is generally reserved for patients who do not respond to Entacapone. * **Discoloration:** A common side effect of COMT inhibitors is the harmless **orange discoloration of urine**.

Q: What is the drug of choice for juvenile myoclonic epilepsy?

Valproate. **Explanation:** **Juvenile Myoclonic Epilepsy (JME)**, also known as Janz syndrome, is a common idiopathic generalized epilepsy characterized by myoclonic jerks (typically in the morning), generalized tonic-clonic seizures (GTCS), and occasionally absence seizures. **Why Valproate is the Correct Answer:** Sodium Valproate is the **drug of choice** for JME because it is a broad-spectrum antiepileptic drug (AED) that effectively controls all three seizure types associated with the syndrome. It works by multiple mechanisms: blocking voltage-gated sodium channels, increasing GABA levels, and inhibiting T-type calcium channels. In JME, Valproate provides a high rate of seizure freedom (up to 80-90%), though it is often required lifelong as relapse rates are high upon discontinuation. **Analysis of Incorrect Options:** * **Phenytoin:** This is a narrow-spectrum AED. It is contraindicated in JME because it can **exacerbate** myoclonic jerks and absence seizures. * **Lamotrigine:** While effective for GTCS, Lamotrigine can sometimes worsen myoclonic seizures in JME patients. It is generally considered a second-line agent or an alternative in females of childbearing age. * **Zonisamide:** This is a broad-spectrum agent that may be used as an adjunct, but it is not the first-line gold standard compared to Valproate. **Clinical Pearls for NEET-PG:** * **Teratogenicity:** While Valproate is the most effective, it is highly teratogenic (Neural Tube Defects). In **females of childbearing age**, Levetiracetam or Lamotrigine are preferred alternatives. * **EEG Finding:** JME typically shows characteristic **4-6 Hz polyspike-and-wave** discharges. * **Avoidance:** Drugs that block sodium channels exclusively (Phenytoin, Carbamazepine, Oxcarbazepine) should be avoided in JME as they aggravate myoclonus.

Question 1

All of the following statements about phenytoin are true except:

Accepted Answer

Cerebellar degeneration occurs on long-term administration

Answer

It follows saturation kinetics

Answer

Anti-seizure activity closely resembles plasma concentration

Answer

Does not depress CNS

Question 2

Lorazepam is preferred over Diazepam in the treatment of status epilepticus because:

Accepted Answer

It has a more sustained action due to lower lipid solubility and slower distribution.

Answer

It has a longer half-life than diazepam.

Answer

It has faster clearance.

Answer

It has more bioavailability.

Question 3

Which of the following effects is specifically observed with intravenous diazepam and not with other routes of administration?

Accepted Answer

Coronary dilatation

Answer

Analgesia

Answer

Sedation

Answer

Hypotension

Question 4

Which of the following drugs is not metabolized by the liver?

Accepted Answer

Oxazepam

Answer

Flunitrazepam

Answer

Diazepam

Answer

Nitrazepam

Question 5

Which of the following does NOT affect the duration of action of local anesthesia?

Accepted Answer

Non-nervous tissue diffusibility

Answer

Protein binding capacity of the local anesthetic

Answer

Addition of a vasoconstrictor

Answer

Vasodilator activity of the local anesthetic

Question 6

Which serotonin-norepinephrine reuptake inhibitor is predominantly used in the condition shown above?

Accepted Answer

Duloxetine

Answer

Venlafaxine

Answer

Citalopram

Answer

Escitalopram

Question 7

All of the following drugs are used for managing status epilepticus except?

Accepted Answer

Carbamazepine

Answer

Phenytoin

Answer

Diazepam

Answer

Thiopentone sodium

Question 8

Which of the following is a long-acting full agonist oral opiate used for heroin detoxification or long-term maintenance?

Accepted Answer

Methadone

Answer

Morphine

Answer

Fentanyl

Answer

None of the above

Question 9

What is the mechanism of action of Tolcapone?

Accepted Answer

COMT inhibitor

Answer

Dopa decarboxylase inhibitor

Answer

MAO - A inhibitor

Answer

MAO - B inhibitor

Question 10

What is the drug of choice for juvenile myoclonic epilepsy?

Accepted Answer

Valproate

Answer

Phenytoin

Answer

Lamotrigine

Answer

Zonisamide

Central Nervous System Pharmacology — MCQs

Central Nervous System Pharmacology — MCQs

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