Aminobenzoic acid derivatives – Benzocaine MCQs With Answer

Aminobenzoic acid derivatives – Benzocaine MCQs With Answer
Benzocaine, an ethyl 4-aminobenzoate ester and a prototypical aminobenzoic acid derivative, is a commonly used topical local anesthetic in pharmacy practice. B. Pharm students should grasp its chemistry, structure-activity relationships (SAR), ester hydrolysis to para-aminobenzoic acid (PABA), metabolism by plasma esterases, pharmacokinetics, formulation types (gels, sprays, lozenges), and safety concerns such as PABA-related hypersensitivity and methemoglobinemia. Understanding analytical methods (HPLC), stability, regulatory considerations, and clinical implications aids rational formulation design and patient counseling. This concise introduction links molecular properties to clinical use and adverse effects. Now let’s test your knowledge with 30 MCQs on this topic.

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

• Ester local anesthetic and PABA derivative
• Amide local anesthetic
• Opioid analgesic
• Nonsteroidal anti-inflammatory

Correct Answer: Ester local anesthetic and PABA derivative

Q2. What is the primary clinical use of benzocaine?

• Topical mucosal and dermal anesthesia
• Intravenous regional anesthesia
• General anesthesia induction
• Systemic analgesia for chronic pain

Correct Answer: Topical mucosal and dermal anesthesia

Q3. How is benzocaine primarily metabolized in the body?

• Hydrolyzed by plasma esterases to para-aminobenzoic acid (PABA)
• Oxidized by cytochrome P450 to inactive metabolites
• Conjugated by glucuronidation in the liver
• Excreted unchanged by the kidneys

Correct Answer: Hydrolyzed by plasma esterases to para-aminobenzoic acid (PABA)

Q4. The most common allergic reaction to benzocaine is due to which mechanism?

• PABA-mediated allergic contact dermatitis
• IgE-mediated anaphylaxis to the ester bond
• T-cell mediated autoimmune destruction of nerves
• Complement activation by impurities

Correct Answer: PABA-mediated allergic contact dermatitis

Q5. Which serious hematologic adverse effect is associated with topical benzocaine?

• Methemoglobinemia
• Agranulocytosis
• Hemolytic anemia due to G6PD deficiency
• Pancytopenia

Correct Answer: Methemoglobinemia

Q6. Why is benzocaine generally not used for injectable local anesthesia?

• Poor water solubility and primary suitability for topical application
• Extremely long systemic half-life making injections unsafe
• Strong vasoconstrictive effect preventing tissue absorption
• Irreversible binding to sodium channels when injected

Correct Answer: Poor water solubility and primary suitability for topical application

Q7. Which statement best describes benzocaine’s solubility?

• Poor water solubility and relatively lipophilic
• Highly water soluble and hydrophilic
• Water-soluble salts are commonly used in formulations
• Soluble only in alkaline aqueous media

Correct Answer: Poor water solubility and relatively lipophilic

Q8. What characterizes the onset and duration of benzocaine’s local anesthetic effect?

• Rapid onset and short duration due to ester hydrolysis
• Slow onset and extremely prolonged duration
• No clinical onset as it is not a true anesthetic
• Delayed onset with cumulative long-lasting effect

Correct Answer: Rapid onset and short duration due to ester hydrolysis

Q9. What is the chemical name of benzocaine?

• Ethyl 4-aminobenzoate (para-aminobenzoate ester)
• 2-(Diethylamino)-N-(2,6-dimethylphenyl)acetamide
• Methyl 3-aminobenzoate
• 4-Amino-2-chlorobenzoic acid

Correct Answer: Ethyl 4-aminobenzoate (para-aminobenzoate ester)

Q10. Which statement about benzocaine ionization at physiological pH is correct?

• It is mostly unionized at physiological pH, facilitating membrane penetration
• It is highly ionized at physiological pH, limiting penetration
• It forms a stable quaternary ammonium ion at pH 7.4
• It exists primarily as an anionic salt in tissues

Correct Answer: It is mostly unionized at physiological pH, facilitating membrane penetration

Q11. What is the primary mechanism of action of benzocaine?

• Blockade of voltage-gated sodium channels in nerve membranes
• Activation of GABA receptors causing neuronal inhibition
• Inhibition of cyclooxygenase enzymes reducing pain mediators
• Agonism at opioid receptors in peripheral nerves

Correct Answer: Blockade of voltage-gated sodium channels in nerve membranes

Q12. In terms of structure-activity relationship (SAR), which modification reduces PABA formation and allergic potential?

• Conversion of the ester linkage to an amide linkage
• Adding a nitro group to the para position of the ring
• Replacing the ethyl group with a methyl ether
• Introducing a tertiary amine into the aromatic ring

Correct Answer: Conversion of the ester linkage to an amide linkage

Q13. Which of the following formulations commonly contains benzocaine?

• Topical gels, sprays, lozenges and creams for mucosal analgesia
• Intravenous infusion bags for surgical anesthesia
• Oral sustained-release tablets for chronic pain
• Subcutaneous implants for long-term analgesia

Correct Answer: Topical gels, sprays, lozenges and creams for mucosal analgesia

Q14. Which analytical technique is commonly used for benzocaine quantitative assay and impurity profiling?

• High-performance liquid chromatography (HPLC)
• Flame photometry
• Acid-base titration
• Non-specific colorimetric urine test

Correct Answer: High-performance liquid chromatography (HPLC)

Q15. Recommended storage conditions for benzocaine-containing topical products typically include:

• Cool, dry place protected from light and moisture
• Storage above 40°C to maintain solubility
• Freezing to stabilize the ester bond
• Continuous exposure to air to prevent degradation

Correct Answer: Cool, dry place protected from light and moisture

Q16. Which co-administered drug class can increase the risk of methemoglobinemia with benzocaine?

• Other oxidizing agents or drugs known to induce methemoglobinemia
• Beta-lactam antibiotics that potentiate ester hydrolysis
• Topical corticosteroids that block esterases
• Proton pump inhibitors that alkalinize tissues

Correct Answer: Other oxidizing agents or drugs known to induce methemoglobinemia

Q17. What pediatric safety advisory is associated with benzocaine topical products?

• Avoid use in children under two years of age due to methemoglobinemia risk
• Recommended as first-line teething remedy for neonates
• Safe for routine use in infants at high concentration sprays
• Contraindicated only in children with food allergies

Correct Answer: Avoid use in children under two years of age due to methemoglobinemia risk

Q18. The preferred acute treatment for severe benzocaine‑induced methemoglobinemia is:

• Intravenous methylene blue administration
• Oral activated charcoal
• High-dose corticosteroids
• Intravenous naloxone

Correct Answer: Intravenous methylene blue administration

Q19. For a patient with known PABA hypersensitivity, which alternative local anesthetic class is preferable?

• Amide local anesthetics such as lidocaine
• Other PABA ester anesthetics
• Topical salicylates for nerve block
• Systemic NSAIDs for local anesthesia

Correct Answer: Amide local anesthetics such as lidocaine

Q20. Systemic toxicity from absorbed benzocaine primarily affects which systems?

• Central nervous system and cardiovascular system via sodium channel effects
• Renal system causing acute tubular necrosis
• Endocrine system causing adrenal suppression
• Musculoskeletal system causing rhabdomyolysis

Correct Answer: Central nervous system and cardiovascular system via sodium channel effects

Q21. Which formulation strategy can enhance benzocaine topical penetration through mucosa?

• Use of solvents or penetration enhancers such as ethanol or propylene glycol
• Formulation as an insoluble suspension without solvents
• Lowering concentration to reduce lipophilicity
• Adding large ionic salts to increase water solubility

Correct Answer: Use of solvents or penetration enhancers such as ethanol or propylene glycol

Q22. The hydrolysis product PABA can have which clinically relevant interaction?

• Antagonizes sulfonamide antibiotics by providing PABA substrate
• Potentiates aminoglycoside nephrotoxicity
• Enhances anticoagulant effect of warfarin
• Inhibits absorption of oral calcium supplements

Correct Answer: Antagonizes sulfonamide antibiotics by providing PABA substrate

Q23. In quality control of benzocaine products, which analytes are typically monitored?

• Benzocaine and its hydrolysis product para-aminobenzoic acid (PABA)
• Only total nitrogen content without specific assay
• Only residual solvents, not the active ingredient
• Trace metals as the primary stability indicator

Correct Answer: Benzocaine and its hydrolysis product para-aminobenzoic acid (PABA)

Q24. Which enzymes are primarily responsible for benzocaine ester hydrolysis?

• Plasma and tissue esterases (e.g., butyrylcholinesterase)
• Cyclooxygenases in inflammatory tissue
Monoamine oxidases in neuronal synapses
• Glutathione-S-transferases in hepatocytes

Correct Answer: Plasma and tissue esterases (e.g., butyrylcholinesterase)

Q25. Which of the following is a clear contraindication for benzocaine use?

• Known hypersensitivity to PABA or history of benzocaine allergy
• Controlled hypertension without skin lesions
• Mild allergic rhinitis controlled with antihistamines
• Stable hypothyroidism on replacement therapy

Correct Answer: Known hypersensitivity to PABA or history of benzocaine allergy

Q26. Regarding benzocaine use for infant teething pain, which statement is correct?

• Its use is discouraged in infants due to methemoglobinemia risk
• It is the recommended first-line teething analgesic for neonates
• High-dose sprays are preferred over gels for infants
• It should be administered systemically for better effect

Correct Answer: Its use is discouraged in infants due to methemoglobinemia risk

Q27. Which key difference distinguishes benzocaine from lidocaine?

• Benzocaine is an ester (topical), while lidocaine is an amide (injectable and topical) with lower allergic potential
• Benzocaine is an amide with hepatic metabolism, lidocaine is an ester hydrolyzed by plasma esterases
• Benzocaine is primarily used intravenously, lidocaine only topically
• Both are identical in chemical class and pharmacokinetics

Correct Answer: Benzocaine is an ester (topical), while lidocaine is an amide (injectable and topical) with lower allergic potential

Q28. Which pH condition accelerates hydrolysis of benzocaine in aqueous formulations?

• Alkaline conditions accelerate ester hydrolysis; acidic conditions favor stability
• Strongly acidic conditions accelerate hydrolysis more than alkaline
• Neutral pH causes the fastest hydrolysis compared to extremes
• Hydrolysis is independent of pH for benzocaine esters

Correct Answer: Alkaline conditions accelerate ester hydrolysis; acidic conditions favor stability

Q29. How does benzocaine’s lipophilicity influence its topical action?

• High lipophilicity increases tissue penetration and topical potency but reduces water solubility
• High lipophilicity prevents any penetration into mucosa
• Low lipophilicity is required for effective topical anesthesia
• Lipophilicity has no effect on topical anesthetic action

Correct Answer: High lipophilicity increases tissue penetration and topical potency but reduces water solubility

Q30. Which diagnostic method is definitive for detecting methemoglobinemia caused by benzocaine?

• Co-oximetry measurement of methemoglobin levels
• Standard pulse oximetry reading alone
• Urine dipstick test for heme
• Complete blood count without specialized testing

Correct Answer: Co-oximetry measurement of methemoglobin levels

G S Sachin

I am a Registered Pharmacist under the Pharmacy Act, 1948, and the founder of PharmacyFreak.com. I hold a Bachelor of Pharmacy degree from Rungta College of Pharmaceutical Science and Research. With a strong academic foundation and practical knowledge, I am committed to providing accurate, easy-to-understand content to support pharmacy students and professionals. My aim is to make complex pharmaceutical concepts accessible and useful for real-world application.

Mail- Sachin@pharmacyfreak.com