The purpose of this study is to determine the absorption and bioavailability of codeine in
relation to postnatal (PNA) and postconceptional (PCA) age; determine the parent drug
(codeine), its active metabolites, their formation rates and their ratios in relation with
PCA and PNA; and identify relevant genetic polymorphisms of opioid metabolism in the study
population and their potential relationship to the biodisposition and pharmacodynamic effects
of codeine. The study population is intubated and mechanically ventilated infants equal to or
greater than 26 weeks gestational age at birth and less than 4 weeks postnatal age.