One of the phrases that trips off of the tongue of most paediatric nurses is that ‘children are not little adults’, but a recent review in Archives of Disease in Childhood looking at drug dosing in children suggests that in this regard at least, they may be. There are two crucial concepts in pharmacology, these being pharmacokinetics (PK), which is what the body does to the drug; and pharmacodynamics (PD), which is what the drug does to the body. The other important issue of course is the desired effect and how this balances against undesirable effects.
The authors suggest that the per Kg doing method probably results in under-dosing of many children, particularly those in the 1-3 year-old age group who have relatively high drug clearance and metabolic rates. Furthermore the relationship between drug clearance and weight is not linear, which may be problematic particularly among obese children as the role that fat plays in drug distribution and clearance differs between different drugs. As if that weren’t enough, there is a third method of assessing maturity, while we are used to thinking of age and weight; the passage of time, (defined as the postmenstrual age) may also be useful measure as this takes account of maturation before birth. All of this leads the authors to conclude that children over the age of 2 years are indeed probably adult-like (yes ‘little adults’) differing only in size; while those under this age, being less mature are immature children.
All of this is rather confusing for the clinical nurse, so what should be done. Firstly there is everyone’s favorite dissertation recommendation – more research. More immediately it may be possible to individualise doses more, taking into account specific covariates, although this may require computer support to allow for the more complex calculations and decision making processes.
However, there is something that everyone can do right now, which is to make treatments explicitly outcome-based, taking into account the benefits and risks of treatments. The authors of the papers give a good example, which is that of opiate analgesia, how specific children may balance the relative importance of pain control and nausea; some might think the first is more important, others might put up with a bit of pain in order not to feel nauseated. The treatment of fever presents another such challenge, what outcome should be aimed for in the treatment of fever with antipyretics, bearing in mind fever is a symptom not a disease; it does not need treating and may even be helpful?
Along with ‘children are not little adults’, another phrase I remember from my student days was the four rights right patient, right drug, right dose, right time; maybe we should add a fifth – right outcome?