Local anesthetic agents MCQs With Answer: This concise, focused set of questions prepares B. Pharm students for clinical and exam applications of local anesthetics. It covers classification (ester vs amide), chemical structure, mechanism of action (voltage-gated sodium channel blockade), pharmacokinetics (absorption, distribution, metabolism by plasma esterases or hepatic CYP450), clinical uses (topical, infiltration, nerve block, spinal, epidural), potency/onset/duration relationships, additives (epinephrine, bicarbonate, hyaluronidase), and major toxicities (CNS, cardiotoxicity, allergy, methemoglobinemia). Each MCQ includes clear options, reasoning for choices, and clinically relevant dosing and safety tips to strengthen pharmacology retention. Now let’s test your knowledge with 30 MCQs on this topic.
Q1. Which structural component of local anesthetic agents primarily determines whether a drug is classified as an ester or an amide?
- The aromatic ring
- The intermediate chain linking the ring and amine
- The tertiary amine
- The pKa value
Correct Answer: The intermediate chain linking the ring and amine
Q2. The primary mechanism of action of most local anesthetics is:
- Enhancement of GABAergic inhibition in the spinal cord
- Blockade of voltage-gated sodium channels, preventing action potential propagation
- Activation of opioid receptors on peripheral nerves
- Inhibition of acetylcholinesterase at the neuromuscular junction
Correct Answer: Blockade of voltage-gated sodium channels, preventing action potential propagation
Q3. Which property most strongly correlates with potency of a local anesthetic?
- pKa
- Lipid solubility
- Protein binding
- Water solubility
Correct Answer: Lipid solubility
Q4. Which factor most directly influences the onset of action of a local anesthetic?
- Lipid solubility
- Protein binding
- pKa relative to tissue pH
- Presence of vasoconstrictor
Correct Answer: pKa relative to tissue pH
Q5. Ester local anesthetics are primarily metabolized by:
- Hepatic CYP450 enzymes
- Renal excretion unchanged
- Plasma pseudocholinesterase (butyrylcholinesterase)
- Intestinal flora
Correct Answer: Plasma pseudocholinesterase (butyrylcholinesterase)
Q6. Which amide local anesthetic is most associated with severe cardiotoxicity, especially after systemic absorption or intravascular injection?
- Lidocaine
- Bupivacaine
- Prilocaine
- Procaine
Correct Answer: Bupivacaine
Q7. Which local anesthetic is an amide but contains an ester group in its structure that facilitates rapid hydrolysis and makes it popular in dentistry?
- Articaine
- Ropivacaine
- Tetracaine
- Chloroprocaine
Correct Answer: Articaine
Q8. Addition of epinephrine to a local anesthetic solution primarily causes:
- Increased systemic absorption and shorter duration
- Vasodilation and more bleeding
- Local vasoconstriction, reduced systemic absorption, and prolonged duration
- Inactivation of the anesthetic by oxidation
Correct Answer: Local vasoconstriction, reduced systemic absorption, and prolonged duration
Q9. Which metabolite of ester local anesthetics is responsible for many reported allergic reactions?
- 4-Aminobenzoic acid (PABA)
- o-Toluidine
- Para-hydroxybenzoate
- Benzoic acid
Correct Answer: 4-Aminobenzoic acid (PABA)
Q10. Which local anesthetic is most commonly implicated in causing methemoglobinemia?
- Lidocaine
- Bupivacaine
- Prilocaine
- Procaine
Correct Answer: Prilocaine
Q11. Which statement about pKa and clinical effect of local anesthetics is correct?
- A lower pKa relative to tissue pH favors more ionized drug and slower onset
- A pKa close to physiologic pH favors a greater fraction of nonionized drug and faster onset
- pKa has no effect on onset; only lipid solubility matters
- Higher pKa always gives longer duration
Correct Answer: A pKa close to physiologic pH favors a greater fraction of nonionized drug and faster onset
Q12. Which nerve fibers are blocked first by local anesthetics during regional anesthesia?
- Large myelinated motor fibers (A-alpha)
- Small unmyelinated C fibers and small myelinated A-delta fibers (pain and temperature)
- Large sensory fibers for proprioception
- All fibers are blocked equally
Correct Answer: Small unmyelinated C fibers and small myelinated A-delta fibers (pain and temperature)
Q13. Which local anesthetic is an ester-type and commonly used for spinal anesthesia in short procedures due to very short duration?
- Procaine
- Chloroprocaine
- Tetracaine
- Lidocaine
Correct Answer: Chloroprocaine
Q14. Which additive can be used to speed the onset of a local anesthetic by increasing the fraction of nonionized drug at the injection site?
- Sodium bicarbonate
- Epinephrine
- Hyaluronidase
- Phenylephrine
Correct Answer: Sodium bicarbonate
Q15. Systemic local anesthetic toxicity typically presents first with:
- Severe bradycardia and asystole
- CNS excitatory symptoms such as tinnitus, circumoral numbness, and seizures
- Delayed hypersensitivity rash
- Hypertension and hyperreflexia
Correct Answer: CNS excitatory symptoms such as tinnitus, circumoral numbness, and seizures
Q16. The recommended first-line therapy for severe local anesthetic systemic toxicity (LAST) with cardiovascular compromise is:
- High-dose benzodiazepines alone
- Intravenous lipid emulsion (lipid rescue) along with advanced cardiac life support
- Intravenous epinephrine boluses only
- Immediate dialysis
Correct Answer: Intravenous lipid emulsion (lipid rescue) along with advanced cardiac life support
Q17. Which amide local anesthetic has a long duration and high protein binding, commonly used for epidurals and prolonged nerve blocks?
- Lidocaine
- Bupivacaine
- Procaine
- Chloroprocaine
Correct Answer: Bupivacaine
Q18. Which local anesthetic is often preferred for labor epidural due to lower motor block and better safety profile in obstetrics?
- Tetracaine
- Ropivacaine
- Benzocaine
- Procaine
Correct Answer: Ropivacaine
Q19. Which local anesthetic is unique because it also has intrinsic vasoconstrictive activity and is used as a topical nasal anesthetic and vasoconstrictor?
- Cocaine
- Lidocaine
- Prilocaine
- Articaine
Correct Answer: Cocaine
Q20. Protein binding of a local anesthetic primarily affects which clinical parameter?
- Onset of action
- Potency only
- Duration of action
- pKa value
Correct Answer: Duration of action
Q21. Which of the following is a major metabolic enzyme system responsible for amide local anesthetic biotransformation?
- Monoamine oxidase (MAO)
- CYP450 hepatic enzymes
- Plasma cholinesterase
- UDP-glucuronyl transferase in plasma
Correct Answer: CYP450 hepatic enzymes
Q22. In a hypotensive patient, the systemic absorption of subcutaneous local anesthetic is expected to be:
- Increased due to vasodilation from hypotension
- Decreased because of reduced regional blood flow
- Unchanged compared to normotension
- Completely prevented
Correct Answer: Decreased because of reduced regional blood flow
Q23. A patient with pseudocholinesterase deficiency would have prolonged effects primarily after administration of which drug?
- Lidocaine
- Procaine
- Bupivacaine
- Ropivacaine
Correct Answer: Procaine
Q24. Which local anesthetic is most appropriate for short procedures requiring quick onset and short duration, such as ambulatory infiltration?
- Chloroprocaine
- Tetracaine
- Bupivacaine
- Articaine
Correct Answer: Chloroprocaine
Q25. Which clinical technique depends on injecting local anesthetic into the subarachnoid space to produce dense sensory and motor blockade?
- Topical anesthesia
- Infiltration anesthesia
- Spinal (subarachnoid) anesthesia
- Peripheral nerve stimulation
Correct Answer: Spinal (subarachnoid) anesthesia
Q26. A common dental local anesthetic known for better bone penetration and increased risk of paresthesia in mandibular blocks is:
- Lidocaine
- Articaine
- Prilocaine
- Procaine
Correct Answer: Articaine
Q27. Which local anesthetic is available as an ointment or spray and is frequently associated with methemoglobinemia when overused topically?
- Benzocaine
- Lidocaine
- Bupivacaine
- Chloroprocaine
Correct Answer: Benzocaine
Q28. Which statement about enantiomers of local anesthetics is true?
- All racemic local anesthetics have identical toxicity as their single enantiomer
- Levo-enantiomers (e.g., levobupivacaine) may have less cardiotoxicity than racemic forms
- Enantiomers have no impact on potency or duration
- Only ester anesthetics have clinically used enantiomers
Correct Answer: Levo-enantiomers (e.g., levobupivacaine) may have less cardiotoxicity than racemic forms
Q29. In hepatic failure, which adjustment is most appropriate for amide local anesthetic use?
- Increase dose because clearance is faster
- Use the same dose; amides are unaffected by liver function
- Reduce dose or choose an ester local anesthetic metabolized by plasma esterases
- Switch to topical therapy only
Correct Answer: Reduce dose or choose an ester local anesthetic metabolized by plasma esterases
Q30. Hyaluronidase is often added to local anesthetic solutions to:
- Reduce toxicity by binding free drug
- Enhance spread of anesthetic through connective tissue and speed onset
- Act as a vasoconstrictor to prolong duration
- Prevent methemoglobinemia
Correct Answer: Enhance spread of anesthetic through connective tissue and speed onset
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