Abstract

No simple formula relating dose to age or body weight has proved satisfactory. The reason is that the dose is largely determined by factors such as lean body mass, extracellular fluid volume and metabolic rate, none of which are linearly related to weight. These factors happen to be much more closely related to the surface area of the body, and many paediatricians use this empirical relationship to estimate doses for children. When this method is used children are seen to be neither more nor less sensitive to most drugs than adults. The few clear-cut exceptions are particularly important in the newborn and in young infants, who are for example less sensitive than adults to phenobarbitone and perhaps other barbiturates, and more sensitive than adults to sulphonamides, opiates, vitamin K analogues, and various antibiotics.