Abstract
Neonates are a heterogeneous population characterised by a limited weight or size range. They are the group of children from birth up to the age of 28 days of life and include both preterm (i.e. born before 37 weeks of gestational age) and term neonates. In practice, the word “neonate” extends to former preterm neonates. Consequently, postmenstrual age (PMA) may range from extreme preterm birth at 22 weeks to 50 weeks PMA, while weight commonly ranges from 0.5 to 5 kg, an entire order of magnitude. Age, size, co-morbidity, coadministration of drugs and genetic polymorphisms contribute to the extensive interindividual pharmacokinetic (PK) and pharmacodynamic (PD) variability in this population. These phenomena distinguish neonates as a specific population with major pharmacological differences from their older counterparts. Although the general principles of clinical pharmacology also apply to neonates, their characteristics warrant a tailored approach. History provides us with evidence of the deleterious effects of drugs in this age group including chloramphenicol (grey baby syndrome) and benzyl alcohol (gasping syndrome) in neonates. Neonatal bupivacaine toxicity in those receiving long-term infusion and acute fentanyl tolerance are two recent anaesthesia examples.