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Neonatal Pharmacokinetics — FRCA Final MCQ

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ModeratePaediatric AnaesthesiaNeonatal PharmacokineticsFRCA Final

A 3-month-old infant (5 kg) with biliary atresia is listed for a Kasai portoenterostomy. His conjugated bilirubin is 180 μmol/L. Which factor most significantly affects the pharmacology of anaesthetic drugs in neonates and young infants?

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Correct answer: C — Higher body water content and larger volume of distribution

Neonates and young infants have a significantly higher proportion of total body water (70-80% vs 55-60% in adults) and a relatively larger extracellular fluid volume. This increases the volume of distribution (Vd) for water-soluble drugs (muscle relaxants, aminoglycosides), requiring higher mg/kg doses for initial effect. Combined with immature hepatic conjugation pathways, reduced protein binding, and relatively high cardiac output, this results in altered drug pharmacokinetics requiring careful dose adjustment.

Reference: RCOA – 2023 – Paediatric pharmacology curriculum; Anderson BJ – 2014 – Paediatric pharmacology