Lidocaine Maximum Dose — FRCA Final MCQ

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ModerateAnaesthetic Equipment & SafetyLidocaine Maximum DoseFRCA Final

A 44-year-old man weighing 80 kg is having a vasectomy under local anaesthesia. The surgeon uses 40 mL of 1% w/v Lidocaine Injection BP without a vasoconstrictor. According to the current SmPC for this preparation, which option gives the maximum single weight-based dose for an adult, before applying the absolute dose cap?

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

Reveal the answer and explanation

Correct answer: D — 4.5 mg/kg

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

D is correct. The specified UK SmPC gives an adult maximum single dose without a vasoconstrictor of 4.5 mg/kg, capped at 300 mg. For this 80 kg patient, 4.5 × 80 = 360 mg, but the absolute cap means that no more than 300 mg should be given. A 1% solution contains 10 mg/mL, so 40 mL contains 400 mg and exceeds the cap by 100 mg. Option A reflects a commonly quoted conservative limit but is not the limit in the specified SmPC. Option B is the paediatric limit stated in this SmPC. Option C applies when lidocaine is combined with a vasoconstrictor, with a separate 500 mg cap. Option E is not the stated adult ceiling. The lowest dose producing adequate anaesthesia should always be used.

Reference: B. Braun Medical. Lidocaine Injection BP 1% w/v, Summary of Product Characteristics, sections 2 and 4.2. https://www.medicines.org.uk/emc/product/15149/smpc