Population pharmacokinetics of oxycodone in plasma and cerebrospinal fluid after epidural and intravenous administration

Objectives: To establish the first plasma and cerebrospinal fluid (CSF) oxycodone population pharmacokinetic (PopPK) model after epidural (EPI) and intravenous (IV) oxycodone administration. Methods: The study was conducted with 30 female subjects undergoing elective gynecological surgery with epidural analgesia. A parallel single dose of EPI oxycodone with IV placebo (EPI group; n = 18) or IV oxycodone with EPI placebo (IV group; n = 12) was administered. An epidural catheter for drug administration was placed at T12/L1 and a spinal catheter for CSF sampling at L3/4. Plasma and CSF for oxycodone analysis were frequently collected. A PopPK model was built using the NONMEM software package. Results: Plasma and CSF oxycodone concentrations were evaluated using separate central plasma and CSF compartments and separate peripheral plasma and CSF compartments. Epidural space served as a depot compartment with transfer to both the plasma and CSF central compartments. The population parameters for plasma clearance and apparent distribution volumes for central and peripheral compartments for plasma and CSF were 37.4 L/h, 90.2 L, 68.9 L, 0.035 L (fixed based on literature), and 0.039 L, respectively. Conclusion: A PopPK model was developed and found to precisely and accurately describe oxycodone time-concentration data in plasma and CSF.

The analgesic efficacy and pharmacokinetics of epidural oxycodone after gynaecological laparotomy: a randomized, double-blind, double-dummy comparison with intravenous administration

AIM

The aim of the present study was to compare the analgesic efficacy of epidural and intravenous (i.v.) oxycodone at the same dose.

METHODS

In this randomized, double-blind, double-dummy clinical trial, 30 women, aged 24-67 years, undergoing elective gynaecological laparotomy, were administrated either i.v. saline and epidural oxycodone 0.1 mg·kg^-1 (EPI group; n = 15) or i.v. oxycodone 0.1 mg·kg^-1 and epidural saline (IV group; n = 15). For multimodal analgesia, patients received i.v. paracetamol and dexketoprofen, and a triple-mixture epidural infusion after the first 4 h postoperatively. The primary outcome was the total dose of i.v. fentanyl for rescue analgesia during the first 4 h postoperatively.

RESULTS

All patients required fentanyl during the first 4 h. The median number of fentanyl doses were three (quartiles 1, 8) in the EPI group and seven (6, 9) in the IV group (mean difference 3.1; 95% confidence interval 0.9, 5.2; P = 0.01). After the first 4 h, the two groups needed a similar total dose of epidural infusion. Patient satisfaction was similarly high in both groups, and both administration routes were well tolerated.

CONCLUSIONS

The data support the superiority of epidural oxycodone compared with that of i.v. administration in pain management after laparotomy.