Ester vs Amide LA — ORE Part 1 MCQ
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Correct answer: C — Procaine
Procaine is an ester local anaesthetic. All other options are amides. Esters (procaine, tetracaine, benzocaine) are characterised by an ester functional group, while amides (lidocaine, prilocaine, mepivacaine, articaine) contain an amide group. This chemical distinction is clinically important: esters are metabolised by plasma cholinesterase and carry a higher risk of sensitising metabolites (eg para-aminobenzoic acid), making them less commonly used. Amides undergo hepatic metabolism. Procaine was historically the first widely used local anaesthetic; though now rarely used in UK dentistry, it remains available and is the correct answer to this fundamental pharmacology classification question.
Reference: Local anaesthetics in interventional radiology: a primer for radiologists on applications and management of complications. PubMed. 2024. https://pubmed.ncbi.nlm.nih.gov/40305878/