Lidocaine Dose Calculation — MFDS Part 1 MCQ

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ModeratePharmacologyLidocaine Dose CalculationMFDS Part 1

A fit and healthy 70 kg adult requires dental local anaesthesia with 2% lidocaine and adrenaline 1:80,000. Using current UK Summary of Product Characteristics dosing for lidocaine with a vasoconstrictor, and before applying any separate adrenaline-related or patient-specific restriction, what is the maximum single dose of the lidocaine component for this patient?

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Correct answer: D — 7.0 mg/kg (490 mg)

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

C is correct. Current UK SmPCs for lidocaine with adrenaline give a weight-related maximum of 7 mg/kg subject to an absolute single adult dose of 500 mg; 7 × 70 = 490 mg, just below that ceiling. A (4.4 mg/kg) is the widely quoted North American dental convention (Malamed) and is sub-maximal under UK licensed dosing, though it remains a sensible conservative clinical working limit. B (2.2 mg/kg) confuses the cartridge volume figure of 2.2 mL with a dose per kilogram. E (1.0 mg/kg) reflects intravenous antiarrhythmic bolus dosing, not infiltration anaesthesia. D (10 mg/kg, 700 mg) exceeds both the weight-based limit and the 500 mg absolute maximum and risks systemic toxicity. In practice fewer cartridges are used, limited by the adrenaline dose, comorbidity and interacting medicines.

Reference: Summary of Product Characteristics: Lidocaine 2% with adrenaline (epinephrine) solution for injection, section 4.2 Posology and method of administration. electronic Medicines Compendium (emc), current version 2025. https://www.medicines.org.uk/emc/product/2396/smpc