The pharmacokinetics of oxycodone is well characterized in children older than six months of age. However, only one study has been published with children younger than six months, concluding that unexplained inter-individual variability is pronounced in the youngest children. The aim of the current study was to quantify oxycodone pharmacokinetics in children ranging from preterm newborn infants to children up to two years of age.

Inclusion Criteria:

• Infants scheduled for surgery with planned perioperative or postoperative opioid analgesia were screened if the gestational age (GA) was at least 23 weeks and postnatal age (PNA) below 2 years

Exclusion Criteria:

• He/she had allergy or hypersensitivity to oxycodone or other ingredients in the formulations or had received monoamineoxidase, CYP3A (cytochrome P450 3A enzymes) or CYP2D6 (cytochrome P450 2D6 enzyme) inhibitors during the previous month or other reason that was considered to contraindicate participation.

Children age from 23 gestational weeks to two years