One of the main problems encountered in clinical pharmacology is the lack of information available for pharmaceutical drugs in paediatric population. As a result, many drugs are used off-label, and the doses are adjusted using empirical algorithms from allometric models optimised for adults. However, this does not take into consideration the different grades of maturation of the organs involved in the absorption, distribution, metabolism and elimination (ADME) processes of drugs in children. To address this problematic two approaches are presented in this thesis: the evaluation of pharmacokinetic predictive models in paediatric population and the use of metabolomics as an innovative tool to differentiate the grades of maturation in paediatrics.