Local Anaesthetic Metabolism — MFDS Part 1 MCQ
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Correct answer: C — Liver
The correct answer is C, the liver. Most amide-type local anaesthetics, including lidocaine and prilocaine, undergo predominantly hepatic metabolism. Their metabolites are subsequently excreted mainly by the kidneys, so renal excretion should not be confused with primary metabolism. Plasma esterases are principally associated with hydrolysis of ester-type local anaesthetics rather than typical amide agents. The lungs and tissues at the injection site influence drug distribution or systemic absorption but are not the principal sites of metabolic clearance. This distinction is clinically relevant because impaired hepatic function or reduced hepatic blood flow can decrease clearance and increase the risk of systemic local-anaesthetic toxicity.
Reference: Electronic Medicines Compendium, EMLA Cream 5% Summary of Product Characteristics, section 5.2 Pharmacokinetic properties, revised 4 June 2026. https://www.medicines.org.uk/emc/product/7994/smpc