Local Anaesthesia — ORE Part 1 MCQ

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ModeratePharmacology & TherapeuticsLocal AnaesthesiaORE Part 1

A 4-year-old child weighing 20 kg requires inferior alveolar nerve block anaesthesia. What is the maximum number of 2.2 mL cartridges of 2% lidocaine with 1:80,000 adrenaline that can be administered?

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Correct answer: E — 3 cartridges

UK eMC SmPC specifies that paediatric patients (1–12 years) receiving lidocaine with adrenaline may receive up to 7 mg/kg as a weight-based guideline. For a 20 kg child, this yields 140 mg maximum. Each 2.2 mL cartridge of 2% lidocaine contains 44 mg. Therefore, 3 cartridges (132 mg) are safe, but 4 cartridges (176 mg) would exceed the limit. Adrenaline allows higher dosing than lidocaine without adrenaline (3 mg/kg), making this a moderate-difficulty item requiring knowledge of both paediatric dosing and cartridge content calculation. Distractor B (2 cartridges) may appeal to candidates who incorrectly apply the 3 mg/kg limit; distractor E (4 cartridges) to those who miscalculate or confuse adult dosing.

Reference: eMC SmPC: Lidocaine with Adrenaline 1:200,000 (paediatric dosing applies to adrenaline-containing formulations). https://www.medicines.org.uk/emc/product/2397/smpc