Background and aims: Oxycodone is one of the most commonly used opioid agonist to treat moderate to severe pain.1 Despite that, the knowledge on epidural administration of oxycodone is sparse. Here we establish a population pharmacokinetic (PopPK) model for oxycodone concentration in plasma and cerebrospinal fluid (CSF) after epidural and intravenous administration.

Methods: 30 women undergoing gynaecological surgery with postoperative epidural analgesia were administered a single dose of oxycodone 0.1 mg/kg either epidurally or intravenously. A spinal catheter was inserted at L3/4 for CSF collection and indwelling venous catheter for plasma collection. A PopPK model for oxycodone was built using the NONMEM software package.

Results: Oxycodone concentrations in plasma and CSF were described using separate central compartments for plasma and CSF, and separate peripheral compartments for plasma and CSF. Epidural space served as a depot compartment with transfer to both central compartments of plasma and CSF.

Conclusions: A PopPK model describes oxycodone time-concentration data with high precision and accuracy. The model can be used for future pharmacodynamic-pharmacokinetic modelling of intravenously and epidurally administered oxycodone.

POPULATION PHARMACOKINETICS OF OXYCODONE AFTER EPIDURAL AND INTRAVENOUS ADMINISTRATION