Dibucaine MCQs With Answer

Introduction — Dibucaine MCQs With Answer

Dibucaine is a potent, long‑acting amide local anesthetic widely studied in B. Pharm pharmacology for its high lipid solubility, strong protein binding, and blockade of voltage‑gated sodium channels. Beyond topical analgesia, dibucaine is central to the “dibucaine number” assay used to detect atypical plasma cholinesterase that prolongs succinylcholine apnea. Understanding its mechanism, pharmacokinetics (hepatic metabolism), clinical uses, toxicity signs (CNS and cardiovascular), and management (including lipid emulsion therapy) is essential for pharmacists. These MCQs emphasize drug action, interactions, metabolism, and clinical implications to deepen your applied knowledge. Now let’s test your knowledge with 30 MCQs on this topic.

Q1. Which class of local anesthetic does dibucaine belong to?

• Amide local anesthetic
• Ester local anesthetic
• Quaternary ammonium anesthetic
• Ketone local anesthetic

Correct Answer: Amide local anesthetic

Q2. What is the primary cellular mechanism of action of dibucaine?

• Blockade of voltage‑gated sodium channels
• Enhancement of GABAergic transmission
• Inhibition of acetylcholinesterase
• Activation of NMDA receptors

Correct Answer: Blockade of voltage‑gated sodium channels

Q3. The dibucaine number is clinically used to detect abnormalities in which enzyme?

• Plasma (pseudo)cholinesterase
• CYP3A4
• Butyryl‑COA dehydrogenase
• Acetaldehyde dehydrogenase

Correct Answer: Plasma (pseudo)cholinesterase

Q4. High lipid solubility of a local anesthetic typically results in which property?

• Increased potency and longer duration
• Faster renal excretion
• Reduced protein binding
• Decreased potency and shorter duration

Correct Answer: Increased potency and longer duration

Q5. Dibucaine is metabolized primarily by which organ system?

• Hepatic microsomal enzymes
• Renal glomerular filtration
• Plasma cholinesterase hydrolysis
• Gastrointestinal microbial metabolism

Correct Answer: Hepatic microsomal enzymes

Q6. Which clinical use is most appropriate for topical dibucaine?

• Topical analgesia for anorectal conditions and minor skin procedures
• Routine intravenous regional anesthesia
• Systemic analgesia for chronic pain
• Primary treatment for bacterial skin infections

Correct Answer: Topical analgesia for anorectal conditions and minor skin procedures

Q7. A low dibucaine number indicates what clinical risk after succinylcholine administration?

• Prolonged neuromuscular blockade (apnea)
• Increased risk of malignant hyperthermia
• Reduced potency of succinylcholine
• Immediate hypersensitivity reaction

Correct Answer: Prolonged neuromuscular blockade (apnea)

Q8. Which of the following factors reduces the effectiveness of local anesthetics like dibucaine in infected tissue?

• Lower tissue pH leading to ionization of the drug
• Increased tissue lipid content
• Higher local protein binding
• Enhanced blood supply improving distribution

Correct Answer: Lower tissue pH leading to ionization of the drug

Q9. Adding epinephrine to a local anesthetic injection primarily causes:

• Prolongation of local anesthetic duration via vasoconstriction
• Acceleration of systemic absorption
• Immediate systemic hypertension without local effects
• Prevention of allergic reactions

Correct Answer: Prolongation of local anesthetic duration via vasoconstriction

Q10. Which adverse effect profile is most characteristic of systemic local anesthetic toxicity?

• CNS excitation (tremor, seizures) followed by depression and cardiovascular collapse
• Isolated renal failure without neurologic signs
• Pure cholinergic overstimulation with bradycardia
• Severe hyperglycemia and ketoacidosis

Correct Answer: CNS excitation (tremor, seizures) followed by depression and cardiovascular collapse

Q11. First‑line immediate management for severe systemic local anesthetic toxicity includes:

• Airway control, oxygenation, seizure control and intravenous lipid emulsion therapy
• High‑dose insulin only
• Immediate hemodialysis
• Administration of naloxone

Correct Answer: Airway control, oxygenation, seizure control and intravenous lipid emulsion therapy

Q12. Compared to ester local anesthetics, amide local anesthetics like dibucaine:

• Are less likely to cause allergic reactions due to absence of PABA metabolites
• Are hydrolyzed rapidly by plasma cholinesterase
• Always have a faster onset
• Are entirely excreted unchanged in urine

Correct Answer: Are less likely to cause allergic reactions due to absence of PABA metabolites

Q13. The onset of action of a local anesthetic is most directly influenced by which property?

• pKa relative to tissue pH
• Protein binding percentage
• Route of hepatic metabolism
• Color and formulation excipients

Correct Answer: pKa relative to tissue pH

Q14. High protein binding of dibucaine contributes primarily to which pharmacokinetic effect?

• Longer duration of action
• Faster renal clearance
• Increased water solubility
• Immediate metabolism by plasma enzymes

Correct Answer: Longer duration of action

Q15. Which statement about the dibucaine inhibition test (dibucaine number) is true?

• Dibucaine inhibits normal pseudocholinesterase strongly but inhibits atypical enzyme poorly
• Dibucaine activates pseudocholinesterase in atypical individuals
• Dibucaine number measures hepatic microsomal activity
• A high dibucaine number indicates abnormal enzyme activity

Correct Answer: Dibucaine inhibits normal pseudocholinesterase strongly but inhibits atypical enzyme poorly

Q16. Which route is NOT a standard clinical administration route for dibucaine?

• Oral systemic therapy for analgesia
• Topical application to skin or mucous membranes
• Localized infiltration for minor procedures (when formulated appropriately)
• Rectal topical formulations for anorectal pain

Correct Answer: Oral systemic therapy for analgesia

Q17. An increased risk of systemic toxicity of dibucaine is expected when it is coadministered with drugs that:

• Inhibit hepatic metabolism (CYP inhibitors), raising plasma levels
• Increase plasma cholinesterase activity
• Reduce CNS sensitivity to seizures
• Enhance renal excretion of lipophilic drugs

Correct Answer: Inhibit hepatic metabolism (CYP inhibitors), raising plasma levels

Q18. Which biochemical feature distinguishes amide local anesthetics like dibucaine from ester types?

• Presence of an amide linkage (-CONH-) between aromatic and intermediate chain
• Hydrolyzable ester bond making them long acting
• Always containing a nitrate functional group
• Being metabolized only by plasma cholinesterase

Correct Answer: Presence of an amide linkage (-CONH-) between aromatic and intermediate chain

Q19. Which lab finding is directly related to a low dibucaine number?

• Decreased inhibition of pseudocholinesterase by dibucaine
• Elevated hepatic transaminases only
• Low serum albumin concentration
• Increased renal creatinine clearance

Correct Answer: Decreased inhibition of pseudocholinesterase by dibucaine

Q20. Which symptom is an early sign of systemic local anesthetic CNS toxicity?

• Tinnitus and perioral numbness
• Anuria and oliguria
• Severe hypotension without neurologic signs
• Diffuse maculopapular rash only

Correct Answer: Tinnitus and perioral numbness

Q21. The potency of dibucaine compared to other local anesthetics is primarily due to:

• High lipid solubility enabling better membrane penetration
• Low molecular weight leading to rapid renal excretion
• Unique activation of opioid receptors
• Presence of a sulfate salt form

Correct Answer: High lipid solubility enabling better membrane penetration

Q22. Which patient factor most commonly prolongs the effect of an amide local anesthetic?

• Hepatic impairment reducing metabolism
• Young age with rapid metabolism
• Concurrent use of metoclopramide enhancing clearance
• High dietary protein intake

Correct Answer: Hepatic impairment reducing metabolism

Q23. Which management strategy reduces absorption and systemic toxicity after inadvertent intravascular injection of a local anesthetic?

• Immediate aspiration before injection and slow incremental dosing with frequent aspiration
• Injecting the entire dose rapidly to minimize tissue exposure time
• Avoiding aspiration as it increases infection risk
• Administering high‑dose oral charcoal

Correct Answer: Immediate aspiration before injection and slow incremental dosing with frequent aspiration

Q24. Methemoglobinemia is most commonly associated with which local anesthetic rather than dibucaine?

• Prilocaine
• Lidocaine
• Bupivacaine
• Procaine

Correct Answer: Prilocaine

Q25. Which lab or genetic test is indicated when a patient has prolonged apnea after succinylcholine?

• Dibucaine number to assess pseudocholinesterase function
• Serum dibucaine concentration measurement
• Urine drug screen for local anesthetics
• Genetic testing for CYP2D6 polymorphism only

Correct Answer: Dibucaine number to assess pseudocholinesterase function

Q26. Why are allergic reactions less frequent with dibucaine compared with ester anesthetics?

• Amide metabolism does not produce para‑aminobenzoic acid (PABA) metabolites
• Dibucaine is injected with antihistamines by default
• It is completely inert and not metabolized
• It lacks any aromatic ring structures

Correct Answer: Amide metabolism does not produce para‑aminobenzoic acid (PABA) metabolites

Q27. In terms of molecular form in tissues, the uncharged (non‑ionized) fraction of dibucaine is important for:

• Crossing nerve membranes to reach intracellular sodium channels
• Binding plasma proteins exclusively
• Being rapidly hydrolyzed by plasma cholinesterase
• Increasing urinary excretion rate

Correct Answer: Crossing nerve membranes to reach intracellular sodium channels

Q28. Which monitoring is most important after administering a large dose of dibucaine regionally?

• Cardiorespiratory monitoring for CNS and cardiovascular toxicity
• Daily liver enzyme testing for the next week
• Immediate MRI to assess tissue penetration
• Continuous blood glucose monitoring

Correct Answer: Cardiorespiratory monitoring for CNS and cardiovascular toxicity

Q29. A pharmacist counseling a patient about topical dibucaine should include which advice?

• Avoid applying to large broken skin areas and seek help if systemic symptoms appear
• Ingest the topical ointment to improve absorption
• Use continuously on open wounds to accelerate healing
• Combine with other topical anesthetics liberally for better effect

Correct Answer: Avoid applying to large broken skin areas and seek help if systemic symptoms appear

Q30. Which statement best summarizes why knowledge of dibucaine pharmacology is important for B. Pharm students?

• It links local anesthetic pharmacodynamics, pharmacokinetics, toxicity management, and clinical laboratory tests like the dibucaine number
• It demonstrates that all local anesthetics are pharmacologically identical
• It shows that topical anesthetics have no systemic risks
• It focuses solely on cosmetic formulation techniques

Correct Answer: It links local anesthetic pharmacodynamics, pharmacokinetics, toxicity management, and clinical laboratory tests like the dibucaine number

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