Paediatric LA Dose Calculation — MFDS Part 1 MCQ

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ModeratePharmacologyPaediatric LA Dose CalculationMFDS Part 1

A healthy three-year-old child weighing 12 kg requires local anaesthesia for a dental procedure. The planned solution is 2% lidocaine with adrenaline, supplied in 2.2 mL cartridges. For this calculation, use a maximum recommended lidocaine dose of 7 mg/kg; 2% lidocaine contains 20 mg/mL. What is the calculated maximum total dose and corresponding volume?

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

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Correct answer: E — 84 mg (4.2 mL; approximately 1.9 cartridges)

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

The correct answer is A. Using the UK SmPC paediatric ceiling of 7 mg/kg for lidocaine with adrenaline, the maximum is 7 × 12 = 84 mg. Since 2% lidocaine contains 20 mg/mL, this equals 4.2 mL, and as each 2.2 mL cartridge holds 44 mg, 84/44 ≈ 1.9 cartridges. Option B applies the more conservative 4.4 mg/kg figure quoted in some non-UK dental texts rather than the stated limit. Options C and E simply state one and half a cartridge without completing the weight-based calculation. Option D (three cartridges, 132 mg) far exceeds the ceiling and risks local anaesthetic systemic toxicity. The maximum is a ceiling, not a target: give the smallest effective dose, reducing further where patient factors dictate.

Reference: Electronic Medicines Compendium (emc). Lidocaine 1% with adrenaline (epinephrine) 1:200,000 solution for injection – Summary of Product Characteristics, section 4.2 Posology (paediatric patients 1–12 years: up to 7 mg/kg with adrenaline). https://www.medicines.org.uk/emc/product/2397/smpc