Lidocaine and anilide derivatives – Lignocaine MCQs With Answer

Lidocaine and anilide derivatives – Lignocaine MCQs With Answer

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Lidocaine (lignocaine) and related anilide derivatives are cornerstone local anesthetics widely covered in B.Pharm curricula. This topic explores their chemical structure (an amide linked to an aniline ring), physicochemical properties (pKa ≈ 7.9, lipid solubility, protein binding), pharmacodynamics (voltage‑gated sodium channel blockade, use‑dependent inhibition), pharmacokinetics (hepatic metabolism to MEGX and GX by CYP enzymes), clinical uses (local anesthesia, antiarrhythmic class IB), formulation strategies (topical, injectable, with epinephrine), and toxicity management (CNS and cardiovascular effects, intralipid therapy). Emphasis is on structure–activity relationships, dosing, and drug interactions. Now let’s test your knowledge with 30 MCQs on this topic.

Q1. What is the chemical class of lidocaine?

  • An ester local anesthetic
  • An anilide (amide) local anesthetic
  • A ketone local anesthetic
  • A sulfonamide local anesthetic

Correct Answer: An anilide (amide) local anesthetic

Q2. Which functional group distinguishes anilide local anesthetics like lidocaine from ester local anesthetics?

  • Carbamate linkage
  • Amide bond (–CONH–)
  • Ester bond (–COO–)
  • Thioether linkage

Correct Answer: Amide bond (–CONH–)

Q3. The primary mechanism of action of lidocaine involves blockade of which channel in neurons?

  • Voltage-gated calcium channels
  • Voltage-gated sodium channels
  • Ligand-gated chloride channels
  • ATP-sensitive potassium channels

Correct Answer: Voltage-gated sodium channels

Q4. Lidocaine shows preferential blockade of which state of the sodium channel?

  • Resting (closed) state only
  • Open and inactivated states (use‑dependent blockade)
  • Only permanently inactivated state
  • Only the refractory state of calcium channels

Correct Answer: Open and inactivated states (use‑dependent blockade)

Q5. Which metabolite of lidocaine is pharmacologically active and used as a marker of hepatic metabolism?

  • Monoethylglycinexylidide (MEGX)
  • Benzocaine
  • PABA (para-aminobenzoic acid)
  • Procaine

Correct Answer: Monoethylglycinexylidide (MEGX)

Q6. Which cytochrome P450 isoforms are primarily involved in lidocaine metabolism?

  • CYP2D6 only
  • CYP1A2 and CYP3A4
  • CYP2E1 only
  • CYP2C9 and CYP2C19

Correct Answer: CYP1A2 and CYP3A4

Q7. The pKa of lidocaine (~7.9) influences onset of action. At physiological pH (~7.4), lidocaine exists mainly as:

  • Unionized (uncharged) form
  • Ionic (protonated) form predominates
  • Completely deprotonated
  • As a free radical

Correct Answer: Ionic (protonated) form predominates

Q8. Adding epinephrine to lidocaine primarily affects its action by:

  • Neutralizing lidocaine’s pH
  • Inducing vasoconstriction to prolong duration and reduce systemic absorption
  • Enhancing metabolic breakdown in liver
  • Converting lidocaine into an ester derivative

Correct Answer: Inducing vasoconstriction to prolong duration and reduce systemic absorption

Q9. Lidocaine is classified as which class of antiarrhythmic agent?

  • Class IA
  • Class IB
  • Class IC
  • Class III

Correct Answer: Class IB

Q10. Which effect on cardiac action potential is typically produced by lidocaine (class IB)?

  • Prolongation of action potential duration
  • Shortening of action potential duration in ischemic tissue
  • Marked slowing of conduction in normal Purkinje fibers
  • Inhibition of potassium efflux increasing refractory period

Correct Answer: Shortening of action potential duration in ischemic tissue

Q11. The maximum recommended dose of lidocaine without epinephrine for infiltration in adults is approximately:

  • 1 mg/kg
  • 4.5 mg/kg
  • 12 mg/kg
  • 20 mg/kg

Correct Answer: 4.5 mg/kg

Q12. Which clinical manifestation is an early sign of systemic lidocaine toxicity?

  • Bradycardia with hypotension only
  • CNS excitation such as tinnitus, circumoral numbness, and metallic taste
  • Immediate cardiac arrest without warning
  • Profound hyperthermia

Correct Answer: CNS excitation such as tinnitus, circumoral numbness, and metallic taste

Q13. In severe systemic local anesthetic cardiotoxicity, which therapy has become a recommended rescue intervention?

  • High-dose epinephrine only
  • Intravenous lipid emulsion (intralipid) therapy
  • Oral activated charcoal
  • Continuous subcutaneous insulin infusion

Correct Answer: Intravenous lipid emulsion (intralipid) therapy

Q14. Lidocaine’s relative potency and duration are influenced mainly by which physicochemical property?

  • Molecular weight only
  • Lipid solubility (oil/water partition coefficient)
  • Number of aromatic rings only
  • Presence of a sulfate group

Correct Answer: Lipid solubility (oil/water partition coefficient)

Q15. Which nerve fibers are most susceptible to lidocaine blockade?

  • Large myelinated A-alpha fibers first
  • Small myelinated A-delta and unmyelinated C fibers (pain and temperature)
  • Only motor fibers
  • Only autonomic efferent fibers

Correct Answer: Small myelinated A-delta and unmyelinated C fibers (pain and temperature)

Q16. Lidocaine is NOT commonly associated with which of the following allergic mechanisms?

  • IgE-mediated allergy from the amide group (rare)
  • Allergic reactions due to para-aminobenzoic acid (PABA) — seen with ester anesthetics
  • Contact dermatitis from preservatives
  • Hypersensitivity to methylparaben preservative

Correct Answer: Allergic reactions due to para-aminobenzoic acid (PABA) — seen with ester anesthetics

Q17. Which structural feature in lidocaine contributes to its classification as an anilide derivative?

  • A para-nitro substituent on the aromatic ring
  • An N-arylamide linkage (aniline ring attached to amide)
  • A tertiary alcohol group attached to the aromatic ring
  • A sulfhydryl side chain

Correct Answer: An N-arylamide linkage (aniline ring attached to amide)

Q18. Lidocaine is often formulated as lidocaine hydrochloride. The HCl salt primarily improves:

  • Skin penetration independent of pH
  • Water solubility and stability
  • Lipid solubility for faster onset
  • Resistance to hepatic metabolism

Correct Answer: Water solubility and stability

Q19. Which of the following increases the fraction of unionized lidocaine and thus speeds onset?

  • Acidic tissue pH
  • Administration with sodium bicarbonate (raised pH)
  • Co-administration with epinephrine alone
  • Lowering local temperature markedly

Correct Answer: Administration with sodium bicarbonate (raised pH)

Q20. Lidocaine topical preparations (patch, gel) are primarily useful because they:

  • Permit systemic delivery for general anesthesia
  • Provide local analgesia with limited systemic absorption
  • Inhibit hepatic CYP enzymes locally
  • Convert lidocaine to its ester metabolite at the skin

Correct Answer: Provide local analgesia with limited systemic absorption

Q21. Compared to ester anesthetics, amide anesthetics like lidocaine are generally:

  • More rapidly hydrolyzed by plasma cholinesterases
  • Less antigenic and more stable to plasma esterases
  • Converted to PABA more readily
  • Completely resistant to hepatic metabolism

Correct Answer: Less antigenic and more stable to plasma esterases

Q22. Which property explains why inflamed or infected tissue often has a slower onset of lidocaine?

  • Increased blood flow washes out lidocaine
  • Lower (acidic) tissue pH increases ionization, reducing membrane penetration
  • Inflammation increases protein binding of lidocaine
  • Inflammation accelerates hepatic metabolism of local drug

Correct Answer: Lower (acidic) tissue pH increases ionization, reducing membrane penetration

Q23. Which laboratory finding is most relevant when monitoring for systemic lidocaine accumulation in patients with hepatic impairment?

  • Serum creatinine only
  • Liver function tests and clinical signs, since hepatic metabolism is primary
  • Serum amylase only
  • Serum sodium concentration only

Correct Answer: Liver function tests and clinical signs, since hepatic metabolism is primary

Q24. Lidocaine’s stereochemistry is best described as:

  • Racemic mixture of two enantiomers
  • Single achiral molecule (no stereocenter)
  • Optically active due to a chiral tertiary carbon
  • Mixture of diastereomers

Correct Answer: Single achiral molecule (no stereocenter)

Q25. Which drug interaction can increase lidocaine plasma concentration by inhibiting its metabolism?

  • Drugs that induce CYP3A4 like rifampicin
  • CYP inhibitors such as cimetidine or some macrolide antibiotics
  • Drugs that bind plasma proteins better than lidocaine only in acidic conditions
  • Topical antifungals with no hepatic effect

Correct Answer: CYP inhibitors such as cimetidine or some macrolide antibiotics

Q26. For management of ventricular arrhythmias in the setting of myocardial ischemia, lidocaine is preferred because it:

  • Increases action potential duration in normal tissue
  • Preferentially affects ischemic tissue and shortens action potential, reducing ectopy
  • Has potent beta-blocking activity
  • Prolongs QT interval safely

Correct Answer: Preferentially affects ischemic tissue and shortens action potential, reducing ectopy

Q27. Which formulation of lidocaine provides prolonged dermal analgesia through occlusive delivery and controlled release?

  • Oral tablet
  • Transdermal patch (e.g., 5% patch)
  • Intravenous bolus only
  • Inhalation aerosol

Correct Answer: Transdermal patch (e.g., 5% patch)

Q28. The primary reason allergic reactions are more common with ester anesthetics than with lidocaine is:

  • Esters generate PABA metabolites that are allergenic
  • Amides are more rapidly metabolized to PABA
  • Lidocaine always contains antihistamines
  • Amide anesthetics form sulfonamide metabolites

Correct Answer: Esters generate PABA metabolites that are allergenic

Q29. Which of the following statements about lidocaine’s protein binding is most accurate?

  • Lidocaine has negligible plasma protein binding
  • Moderate plasma protein binding (≈ 60–80%) influencing free drug levels
  • Extremely high protein binding (>99%) like warfarin
  • Protein binding is not relevant to its pharmacokinetics

Correct Answer: Moderate plasma protein binding (≈ 60–80%) influencing free drug levels

Q30. In designing structure–activity relationships for anilide local anesthetics, increasing lipophilicity mainly results in:

  • Decreased potency but faster onset
  • Increased potency and often longer duration of action
  • Complete resistance to metabolic degradation
  • Loss of sodium channel blocking activity

Correct Answer: Increased potency and often longer duration of action

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