Extradural opioids for postoperative analgesia. A double-blind comparison of pethidine, fentanyl and morphine.

Pethidine 50 mg, fentanyl 100 microgram and morphine 2 mg administered to the extradural space, were compared in the treatment of pain following surgery. All three drugs produced a rapid decrease in pain scores as assessed using a visual linear analogue, morphine being the least effective. Fentanyl had a relatively short duration of action (2 h), whereas morphine appeared to be the longest acting. It is suggested that the best relief of pain would be obtained by incremental doses given extradurally. All drugs produced an increase in sedation, but there was no respiratory depression as assessed by PaCO2 measurement.