The problems in scaling adult drug doses to children

Trevor N Johnson ^1*

¹ Sheffield Children's Hospital, United Kingdom

^* To whom correspondence should be addressed. E-mail: t.johnson{at}simcyp.com.

Accepted 26 February 2007

Abstract

ObjectiveMany drugs are unlicensed in children and consequently many doses have been scaled down from those used in adults. The aim of the current study was to compare the performance of three scaling models in predicting maintenance doses in paediatric subjects from those in adults.

MethodsThree scaling models based on body weight (BW), body surface area (BSA) and BW^0.75 were used to predict maintenance doses across the paediatric age band from the equivalent adult doses for 30 different drugs. The predicted doses were compared to those in the British National Formulary for children 2006 (BNFc). The percentage error and mean squared prediction error were used as a measure of precision while the mean prediction error was used as a measure of bias.

ResultsIn the 1 and 12 month age groups the different approaches ranked on their bias (least bias first) were BW<BW^0.75<BSA and on their precision (most precise first) were BW> BW^0.75>BSA. The BSA and BW^0.75 methods predicted doses up to 2.86- fold higher than BNFc in the 1 month and 1 year age group. In the 7 and 12 year age groups, BW^0.75 and BSA performed better than BW for precision and bias and no predictions were more than 1.5- fold higher than BNFc. The BW method tended to also under-predict dose across the paediatric age range.

ConclusionsDose scaling should only be used as a last resort in determining a suitable dose in children and no single method was suitable across the entire paediatric age range.

Keywords: allometric scaling, body size, drug dose, pediatrics

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