• General Paediatrics
• Growth
• Measurement
• Therapeutics

Body weight (BW) is one of most important measurements in paediatric medicine. In addition to being one of the first parameters announced at the birth of a child in the developed world, BW is used to determine intravenous fluid requirements, shock voltage administered during cardio-respiratory arrest, endotracheal tube size and to assess nutritional status. In prepubertal children, height, age and BW represent co-migrating anthropometric surrogates which are predictive of organ function including the liver and kidney1 (figure 1) and by inference, the function of physiologic processes which collectively determine drug disposition.2 It has been previously stated3 that the BW-based dosing approach has its origins in the Kleiber principle4 which makes the following basic assumptions: (1) that total BW correlates with organ size and hence function and (2) that basal metabolism is proportional to the BW raised to the 0.75 power (BW^0.75). Old, previously applied standard approaches for paediatric drug dosing such as Clark's rule (eg, Infant dose=(BW_infant /BW_adult) Adult dose) have been largely abandoned in that a simple proportionality of BW between a child and an adult does not accurately reflect the nonlinearity in the relationship between BW and the age-dependent changes in drug disposition.2

The safe administration of medicines to children relies on an ability to correctly calculate the drug dose5 and accurately measure and administer a given drug formulation. Given that the majority of paediatric drug doses are calculated on a milligram or microgram per kilogram bodyweight basis, it is essential that the prescriber and/or healthcare provider have an accurate determination of the child's …