LA Protein Binding — MFDS Part 1 MCQ

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ModeratePharmacologyLA Protein BindingMFDS Part 1

When comparing otherwise similar local anaesthetic agents under equivalent clinical conditions, a higher degree of protein binding most strongly predicts which property?

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Correct answer: D — Duration of action

Explanation lettering: C = shown as A · D = shown as B · E = shown as C · A = shown as D · B = shown as E

A is correct. Greater protein binding correlates with a longer duration of local anaesthetic action because the drug is retained at tissue and sodium-channel binding sites for longer. Bupivacaine is extensively protein bound and is long acting. Onset is determined principally by pKa and the proportion present as unionised base at tissue pH, so B is incorrect. Intrinsic potency correlates mainly with lipid solubility, excluding C. Toxicity depends on factors including dose, inadvertent intravascular administration, systemic absorption and agent-specific cardiac and neurological effects, rather than being determined primarily by protein binding. Metabolism is governed mainly by chemical class: ester local anaesthetics undergo plasma hydrolysis, whereas amides are predominantly metabolised hepatically.

Reference: Local anaesthetics. Annals of The Royal College of Surgeons of England (review; physicochemical determinants of onset, potency and duration), 2012. https://publishing.rcseng.ac.uk/doi/10.1308/003588412X13171221502185