The effects of catecholamines are difficult to predict. The between-subject variability observed in clinical setting is multifactorial including constitutional and acquired characteristics of each individual. Epinephrine and norepinephrine dosages are usually extrapolated from adult data. Yet, age is a source of high variability due to development- related phenomena. A population model of epinephrine or norepinephrine was developed in haemodynamically critically ill children. This allowed to identify between-subject variability factors as well as to propose individualized dosage regimens of these two catecholamines according to the desired effect and child characteristics. Epinephrine pharmacokinetics in 39 children at high risk of postoperative low cardiac output syndrome followed a one-compartment model. Clearance increased with bodyweight according to the allometric rule. The resulting increases in heart rate and mean arterial pressure followed a direct Emax model. These were related to age and illness severity. A turn-over model described the increases in blood glucose and lactate. Norepinephrine pharmacokinetics in 38 hypotensive critically ill children followed a one compartment model. Clearance increased with bodyweight (allometry). The resulting increase in mean arterial pressure followed a direct Emax model. This was a function of age and illness severity. The dosage of epinephrine and norepinephrine in children should take into account the bodyweight, age and illness severity of the patient: the younger the child and the more serious the condition, the higher the dosage in order to meet the haemodynamic goals.
