Clinical evidence for different narcotic receptors and relevance for the clinician

Epidural oxycodone or morphine following gynaecological surgery †

BACKGROUND

The analgesic action of oxycodone is of rapid onset, in contrast to morphine, and is mediated by kappa-opioid receptors of the spinal cord. We compared analgesia and side-effects of epidural oxycodone with those of morphine after gynaecological surgery.

METHODS

We studied prospectively in 75 women in a double-blind, randomized manner: epidural morphine 6 mg day(-1) (n=25), epidural oxycodone 6 mg day(-1) (n=25) and epidural oxycodone 12 mg day(-1) (n=25). All patients underwent gynaecological surgery under general (isoflurane and nitrous oxide) and epidural anaesthesia. Visual analogue scale (VAS) pain scores at rest and on coughing, verbal descriptive scale (VDS) satisfaction scores, sedation scores, pruritus scores and nausea/vomiting scores were recorded for 3 days after surgery.

RESULTS

VAS pain scores at rest in patients who received oxycodone 6 mg day(-1) were higher than in patients who received morphine 6 mg day(-1) at 6 h and on the first postoperative day and were significantly higher than in patients who received oxycodone 12 mg day(-1) on the first postoperative day. Scores for nausea, vomiting and pruritus in patients who received oxycodone 6 mg day(-1) and 12 mg day(-1) were lower than those in patients who received morphine. No significant differences were seen in VAS at cough and VDS satisfaction scores between the three groups.

CONCLUSION

Epidural oxycodone was as effective as morphine at the doses investigated, with fewer side-effects.

Respiratory depression and spinal opioids

Administration of epidural and intrathecal opioids may provide excellent postoperative analgesia, but a minority of patients will suffer dangerous respiratory depression. This review discusses the detection and measurement of respiratory depression and summarizes the relevant literature as it pertains to epidural and intrathecal opioid administration. The respiratory depressant effects and pharmacokinetics of spinal opioids are reviewed. The clinical implications and areas of future investigation are discussed.