[Postoperative pain therapy with 1-methadone and metamizole. A randomized study within the scope of intravenous on-demand analgesia].

Methadone, a potent long-acting opioid analgesic, is only seldom prescribed for postoperative pain relief in Germany. It was the aim of the present investigation to evaluate its efficacy and to establish an adequate dose range using intravenous patient-controlled analgesia (PCA), as well as to determine possible drug interactions with the antipyretic analgesic metamizol (dipyrone). 120 patients recovering from elective major abdominal, gynaecological or orthopaedic surgery under standardized balanced anaesthesia were randomly allocated to three groups to self-administer intravenous 1-methadone. Demand doses were 0.573 mg (group LD), 1.145 mg (group HD) or 0.573 mg to which 50 mg metamizol (dipyrone) were added (group LM). Infusion rate was set to 0.137 mg 1-methadone/h in every group, lockout time was 1 min. Hourly maximum dose was set to 5.95 mg 1-methadone/h. During an average PCA duration of 21 hours patients demanded mean dosages of 16.4 mg (LD), 18.7 mg (HD) or 13.4 mg (LM) 1-methadone. Although individual variation in drug consumption was high, effective pain relief was possible in all cases. Cardiovascular and respiratory status during the observation period was always normal. 88-93% of patients preferred PCA in comparison with earlier experienced conventional postoperative pain treatment. It is concluded that patients are able to control adequate drug consumption, i.e. to avoid overdosage, by adjusting demand frequency if variable demand dosages are offered. Thus 13-19 mg 1-methadone per day can be recommended as reasonable dose range for pain relief during the early postoperative period.(ABSTRACT TRUNCATED AT 250 WORDS)