COMPARISON OF EFFECTS OF INTRAOPERATIVE AND POSTOPERATIVE METHADONE: ACUTE TOLERANCE TO THE POSTOPERATIVE DOSE?

The effects of methadone 10 mg administered in two differentclinical contexts, at induction of anaesthesia and followingoperation, were studied in two groups of patients undergoingelective total hip replacement. The intraoperative group receivedmethadone 10 mg i.v. at induction of anaesthesia as part ofa balanced anaesthetic technique. The postoperative group receivedmethadone 10 mg i.v. following operation, extradural bupivacainebeing used for the operative period. A demand analgesia systemdelivering methadone i.v. was used after operation in both groups.Arterial blood-gas tensions, cortisol and glucose concentrations,analgesic effects and plasma methadone concentrations were comparedin the two groups. The only major difference between the twogroups was in analgesic requirement. At the time of connectionto the demand system the two groups had the same plasma methadoneconcentrations. Subsequently, the postoperative group had asignificantly greater analgesic requirement which resulted insignificantly greater plasma methadone concentrations the followingmorning. Thus, the administration of methadone following operationappeared to exert less analgesic effect than the same dose givenduring operation. The reasons for this are discussed.