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Lignocaine maximum dose with adrenaline — FRCA Primary MCQ

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HardPharmacologyLignocaine maximum dose with adrenalineFRCA Primary

A 70 kg patient requires wound infiltration with lignocaine and adrenaline before awake arterial line placement and skin closure. The trainee asks why adrenaline allows a larger total dose. Which explanation is best?

Educational content. Not a substitute for clinical judgement or local policy.

Reveal the answer and explanation

Correct answer: E — Reduced systemic uptake from vasoconstriction

Adrenaline causes local vasoconstriction, reducing systemic absorption and prolonging local anaesthetic action. It does not increase renal clearance, and lignocaine is primarily metabolised in the liver. It does not reverse sodium channel blockade; it reduces peak plasma concentration. Dose calculations still require attention to patient weight, site vascularity and comorbidity.

Reference: Peck, Hill & Williams Pharmacology for Anaesthesia and Intensive Care