Central Nervous System Pharmacology Practice Questions

Q: Which group of afferent fibers is most sensitive to local anesthetics?

Group B fibers. ***Group B fibers***- These are **small, myelinated preganglionic autonomic fibers** that are the **MOST sensitive** to local anesthetics [1].- Their **small diameter combined with myelination** makes them highly susceptible to blockade at the **nodes of Ranvier**.- The classic order of sensitivity is: **B > C > A-delta > A-gamma > A-beta > A-alpha** [1].*Group C fibers*- These are **unmyelinated, small-diameter fibers** transmitting **dull pain and temperature** sensations.- They are the **second most sensitive** to local anesthetics after B fibers.- While their small diameter makes them susceptible, the lack of myelination means blockade occurs more slowly than in B fibers.*Group A fibers*- This group includes **large-diameter, myelinated fibers** (A , A , A , A ) transmitting motor, proprioception, touch, and sharp pain signals.- Their **larger diameter** provides **greater resistance** to local anesthetic blockade.- A-delta fibers (sharp pain) are more sensitive than other A fibers but still less sensitive than B and C fibers.*Group D fibers*- There is **no standard "Group D"** fiber classification in neurophysiology.- The standard classifications are **A (alpha, beta, gamma, delta), B, and C fibers** based on diameter and myelination status.

Q: Which of the following drugs can be used as a transdermal patch for the treatment of Parkinson's disease?

Rotigotine. ***Rotigotine*** - **Rotigotine** is a **dopamine agonist** that is formulated as a **transdermal patch** for continuous delivery, improving compliance and reducing "off" times in Parkinson's disease. - The patch provides steady drug levels, minimizing motor fluctuations often seen with oral medications. *Levodopa* - Levodopa is the **most effective drug** for Parkinson's, but it's administered **orally** and has a short half-life, requiring frequent dosing. - While it can be combined with carbidopa/benserazide to prevent peripheral conversion, it is not available as a transdermal patch. *Apomorphine* - Apomorphine is a **potent dopamine agonist** used for rapid relief of "off" episodes; however, it is administered via **subcutaneous injection**. - It is not available in a transdermal patch formulation due to its chemical characteristics and rapid action. *Selegiline* - **Selegiline** is a **MAO-B inhibitor** that slows the breakdown of dopamine and is used as an adjunct in Parkinson's, and is available in **oral** and **sublingual forms**. - While it has transdermal formulations for depression (e.g., Emsam), it is not used as a patch for Parkinson's disease treatment.

Q: Which of the following local anesthetic agents is a vasoconstrictor?

Cocaine. ***Cocaine*** - Cocaine is unique among local anesthetics as it is a potent **vasoconstrictor**, inhibiting **norepinephrine reuptake** at nerve terminals. - This vasoconstrictive property reduces bleeding and prolongs its anesthetic effect, but also contributes to its cardiotoxicity. *Lignocaine* - Lignocaine (Lidocaine) is an **amide-type local anesthetic** that causes **vasodilation**, which can lead to increased systemic absorption and a shorter duration of action [1]. - Due to its vasodilatory effect, **epinephrine** is often added to lignocaine to limit systemic absorption, prolong its effect, and reduce bleeding [1]. *Bupivacaine* - Bupivacaine is a long-acting **amide-type local anesthetic** that typically causes **vasodilation**, similar to lignocaine. - Its high potency and long duration of action make it suitable for local infiltrations and epidural anesthesia, but it also increases the risk of **cardiotoxicity** [1]. *Tetracaine* - Tetracaine is a potent and long-acting **ester-type local anesthetic** that also causes **vasodilation**. - It is primarily used for **spinal anesthesia** and topical applications and is usually combined with vasoconstrictors to prolong its effect.

Q: Secobarbital is what type of barbiturate?

Short acting barbiturate. ***Short acting barbiturate*** - **Secobarbital** is classified as a short-acting barbiturate, with an onset of action of 15-30 minutes and a duration of 3-6 hours. - Due to its rapid onset and relatively short duration, it has been used as a **sedative-hypnotic** for inducing sleep. *Long acting barbiturate* - **Long-acting barbiturates** like **phenobarbital** have a prolonged duration of action, typically lasting 10-16 hours. - They are primarily used as **antiepileptics** due to their sustained effects. *Intermediate acting barbiturate* - **Intermediate-acting barbiturates** such as **amobarbital** have durations of action between 6-10 hours. - They were historically used for insomnia, but their use has declined due to safer alternatives. *Ultra short acting barbiturate* - **Ultra-short-acting barbiturates** like **thiopental** have an extremely rapid onset (seconds) and very short duration (minutes). - They are mainly used for **induction of anesthesia** due to their quick action and rapid redistribution.

Q: Which of the following statements is incorrect about morphine use?

It can be used in Head injury. ***It can be used in Head injury*** - Morphine is generally **contraindicated** in patients with **head injuries** due to its potential to **increase intracranial pressure**, mask neurological signs, and cause respiratory depression. - The elevated CO2 levels from respiratory depression can lead to cerebral vasodilation, further exacerbating intracranial pressure. *It can be used in Hypotension but with caution* - Morphine can cause **histamine release** and **vasodilation**, potentially worsening existing hypotension. - While possible, it requires careful monitoring and often necessitates concomitant use of **vasopressors** in hypotensive patients. *It can be used in diabetes mellitus* - Morphine use is generally considered safe in patients with **diabetes mellitus**, as it does not directly interfere with glucose metabolism or insulin sensitivity. - However, **renal impairment**, common in long-standing diabetes, can affect morphine excretion and necessitate dose adjustments. *It can be used for severe pain management in selected patients* - Morphine is a potent **opioid analgesic** and is highly effective for managing severe pain in various clinical settings. - Its use is indicated when other less potent analgesics are insufficient, and it is crucial to select patients carefully based on their overall health and potential for adverse effects.

Q: Methemoglobinemia is seen with which of the following agents?

Prilocaine. ***Correct: Prilocaine*** - **Prilocaine** is a local anesthetic known to cause **methemoglobinemia**, especially at higher doses or in susceptible individuals - It metabolizes into **ortho-toluidine**, which oxidizes hemoglobin to methemoglobin - This is a well-recognized adverse effect, particularly when doses exceed 600 mg or in susceptible populations *Incorrect: Tetracaine* - While a local anesthetic, **tetracaine** is not typically associated with causing **methemoglobinemia** - Its primary concern is often related to **systemic toxicity** if absorbed in large quantities *Incorrect: Bupivacaine* - **Bupivacaine** is a widely used local anesthetic, but it is not a common cause of **methemoglobinemia** - It is more famously associated with **cardiotoxicity** at high systemic concentrations *Incorrect: Procaine* - **Procaine** is an ester-type local anesthetic with a lower incidence of systemic toxicity and is not known to cause **methemoglobinemia** - It is more often associated with **allergic reactions** due to its metabolite, **para-aminobenzoic acid (PABA)**

Q: Entacapone acts by inhibiting which of the following enzyme?

COMT. ***Correct: COMT*** - **Entacapone** is a selective, reversible **COMT (Catechol-O-Methyltransferase) inhibitor** [1], [2] - Acts **peripherally** (does not cross blood-brain barrier) [1], [2] - Used as **adjunct to levodopa/carbidopa** in Parkinson's disease [2] - **Mechanism:** Prevents peripheral conversion of levodopa to 3-O-methyldopa, thereby **increasing levodopa bioavailability** and prolonging its duration of action [1], [2] - Reduces "wearing-off" phenomenon in Parkinson's patients [2] *Incorrect: MAO-A* - Monoamine oxidase-A metabolizes dopamine, norepinephrine, and serotonin - **Moclobemide** is a reversible MAO-A inhibitor (antidepressant) - Not the mechanism of entacapone *Incorrect: MAO-B* - Monoamine oxidase-B preferentially metabolizes dopamine in the CNS - **Selegiline and rasagiline** are MAO-B inhibitors used in Parkinson's disease [2] - These work centrally, unlike entacapone which is peripheral [2] *Incorrect: Decarboxylase* - DOPA decarboxylase converts levodopa to dopamine - **Carbidopa and benserazide** are decarboxylase inhibitors (given with levodopa) [2] - Entacapone works downstream by inhibiting COMT, not decarboxylase

Q: What is the preferred concentration range of lidocaine for topical anesthesia?

2-4%. ***Correct Option: 2-4%*** - **Lidocaine** is an **amide-type local anesthetic** commonly used for topical anesthesia to numb localized areas before minor procedures. - The **preferred concentration range for topical application is 2-4%**, which provides effective anesthesia with an acceptable safety profile. - **2% lidocaine gel/cream** is commonly used for skin and genital mucosa. - **4% lidocaine** is standard for oral and respiratory mucous membranes. - **5% lidocaine patches** are used for post-herpetic neuralgia. - This concentration range balances **clinical efficacy** with **minimal systemic toxicity risk**. *Incorrect Option: <2%* - Concentrations below **2%** are generally **suboptimal** for achieving significant topical anesthesia. - These lower concentrations result in **insufficient pain relief** or require longer application times. - While 0.5-1% solutions exist, they are primarily used for infiltration anesthesia, not topical application. *Incorrect Option: 7-12%* - Concentrations in the **7-12%** range are **too high** for routine topical use and increase the risk of **systemic toxicity**. - These concentrations are not standard in clinical practice for general topical anesthesia. - Higher concentrations increase absorption without proportional improvement in efficacy. *Incorrect Option: 12-15%* - Concentrations in the **12-15%** range are **excessively high** and pose substantial **risk of systemic absorption and toxicity**. - Such high concentrations are **not recommended** for topical anesthesia in clinical practice. - Even 10% sprays (used for oropharyngeal anesthesia) require strict dose limitations to prevent toxicity.

Q: A patient has frequent migraine attacks. Which of the following drugs is recommended for prophylaxis?

Propranolol. **Correct: Propranolol** - Propranolol is a **beta-blocker** commonly used for **migraine prophylaxis** [1] - It is **FDA-approved** and considered a **first-line agent** for preventing migraine attacks [1] - It works by reducing the frequency and severity of migraine attacks through its effects on vascular tone and neuronal excitability [1] *Incorrect: Pindolol* - Pindolol is a beta-blocker but is **less effective for migraine prophylaxis** compared to propranolol - It has **intrinsic sympathomimetic activity (ISA)**, which reduces its efficacy in preventing migraines - Not a preferred agent for migraine prevention *Incorrect: Ergotamine* - Ergotamine is used for **acute treatment** of migraine attacks, **not for prophylaxis** [2] - It works by constricting blood vessels and is a vasoconstrictor [2] - **Not suitable for daily preventive use** due to potential side effects, risk of ergotism, and medication overuse headaches (rebound headaches) [2] *Incorrect: None of the options* - This option is incorrect because **propranolol** is a well-established and recommended drug for migraine prophylaxis according to current guidelines

Q: Which of the following drugs can cause hypotension by releasing histamine from mast cells?

Morphine. ***Correct Option - Morphine*** **Morphine** and other opioids can cause **non-immunologic histamine release** from mast cells, leading to **vasodilation**, bronchoconstriction, and systemic hypotension. - The release of histamine directly causes a decrease in **peripheral vascular resistance**, contributing to a drop in blood pressure - This is a **direct pharmacological effect**, not an allergic reaction - Other opioids with similar effects include **codeine** and **meperidine** *Incorrect Option - Procaine* **Procaine** is a local anesthetic that can cause hypotension primarily due to its **direct vasodilatory effect** and cardiovascular depression, rather than histamine release. - While allergic reactions to procaine (which involve histamine) can occur, hypotension in this context is usually related to **systemic absorption** and cardiovascular depression - The mechanism is NOT direct mast cell degranulation *Incorrect Option - Sulfadiazine* **Sulfadiazine** is an antibiotic that may cause hypotension as part of an **allergic reaction** (e.g., anaphylaxis), which would involve histamine. - However, it does not typically cause **direct, non-immunologic histamine release** from mast cells as a primary mechanism - Any histamine release would be **immunologic** (allergic), not direct pharmacological mast cell degranulation *Incorrect Option - Aspirin* **Aspirin** (acetylsalicylic acid) can cause significant hypotension in cases of **overdose** or severe intolerance. - Primary mechanism involves **prostaglandin synthesis inhibition**, which can influence vascular tone - May cause cardiovascular depression in overdose - Does NOT cause direct histamine release from mast cells

Question 1

Which group of afferent fibers is most sensitive to local anesthetics?

Accepted Answer

Group B fibers

Answer

Group A fibers

Answer

Group C fibers

Answer

Group D fibers

Question 2

Which of the following drugs can be used as a transdermal patch for the treatment of Parkinson's disease?

Accepted Answer

Rotigotine

Answer

Apomorphine

Answer

Levodopa

Answer

Selegiline

Question 3

Which of the following local anesthetic agents is a vasoconstrictor?

Accepted Answer

Cocaine

Answer

Lignocaine

Answer

Bupivacaine

Answer

Tetracaine

Question 4

Secobarbital is what type of barbiturate?

Accepted Answer

Short acting barbiturate

Answer

Long acting barbiturate

Answer

Intermediate acting barbiturate

Answer

Ultra short acting barbiturate

Question 5

Which of the following statements is incorrect about morphine use?

Accepted Answer

It can be used in Head injury

Answer

It can be used in Hypotension but with caution

Answer

It can be used in diabetes mellitus

Answer

It can be used for severe pain management in selected patients

Question 6

Methemoglobinemia is seen with which of the following agents?

Accepted Answer

Prilocaine

Answer

Tetracaine

Answer

Bupivacaine

Answer

Procaine

Question 7

Entacapone acts by inhibiting which of the following enzyme?

Accepted Answer

COMT

Answer

MAO-A

Answer

MAO-B

Answer

Decarboxylase

Question 8

What is the preferred concentration range of lidocaine for topical anesthesia?

Accepted Answer

2-4%

Answer

7-12%

Answer

12-15%

Answer

<2%

Question 9

A patient has frequent migraine attacks. Which of the following drugs is recommended for prophylaxis?

Accepted Answer

Propranolol

Answer

None of the options

Answer

Pindolol

Answer

Ergotamine

Question 10

Which of the following drugs can cause hypotension by releasing histamine from mast cells?

Accepted Answer

Morphine

Answer

Sulfadiazine

Answer

Procaine

Answer

Aspirin

Central Nervous System Pharmacology — MCQs

Central Nervous System Pharmacology — MCQs

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