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Local anaesthetic sodium channel blockade — FRCA Primary MCQ

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ModeratePharmacologyLocal anaesthetic sodium channel blockadeFRCA Primary

A 34-year-old patient becomes agitated with perioral numbness and metallic taste after an interscalene block. The anaesthetist suspects early systemic local anaesthetic toxicity. Which cellular action best explains the intended nerve block?

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Correct answer: C — Voltage-gated sodium channel blockade from the intracellular side

Local anaesthetics block voltage-gated sodium channels, preferentially from the intracellular side, preventing action potential propagation. Chloride channel activation describes drugs such as benzodiazepines and propofol more closely. Presynaptic acetylcholine release inhibition is the action of botulinum toxin. The pearl is that systemic toxicity reflects the same sodium-channel effects in the CNS and heart.

Reference: RCoA Primary FRCA Syllabus 2026; Peck, Hill & Williams Pharmacology for Anaesthesia