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The aim of the study was to establish whether there exists a relationship between blood methadone concentration and analgesic response and the intrasubject and intersubject variability in this relationship. Sixteen general surgical (upper abdominal) and orthopedic (spinal fusion) patients were administered methadone (20 mg, iv) as part of the general anesthetic and supplementary methadone doses (usually 5 mg, iv) in the recovery ward until postoperative pain was controlled effectively. The criteria established for the administration of supplementary methadone doses were the co-existence of 1) spontaneous reporting of significant pain by the patient; 2) an unstimulated respiratory rate of greater than 10 breaths/min, and 3) no significant depression of the level of consciousness. A median of two supplementary iv methadone doses (range 1-3) were administered to the patient by a titration method in the recovery ward to obtain effective pain control. This was achieved by a median dose of 10 mg (range 5-20 mg) in addition to the 20 mg intraoperative dose. Serial blood samples were collected for the estimation of blood methadone concentration following all doses. The methadone concentration in the blood sample collected immediately prior to a supplementary dose was termed the minimum effective concentration (MEC [methadone]). The mean (+/- SD) coefficient of variation in MEC (methadone) for the 16 patients was 21 +/- 10% (range: 7-38%), while the mean MEC for methadone was 57.9 +/- 15.2 ng/ml (range: 34.5-80.3 ng/ml) in these patients.(ABSTRACT TRUNCATED AT 250 WORDS)

This study reports the results of a double-blind, parallel-group comparison of intravenous methadone with morphine for the control of postoperative pain. Twenty patients (ASA Status 1 or 2) undergoing a surgical procedure involving an upper abdominal incision were randomly allocated to the methadone (n = 10) or morphine (n = 10) treatment groups. The patients were administered a 20-mg intraoperative opioid dose and 5-mg intravenous increments of opioid from precoded syringes in response to pain in the recovery and surgical wards. There was no significant difference between the mean +/- SD amount of supplementary methadone (8 +/- 6.3 mg) and morphine (9 +/- 9 mg) required in the recovery ward to provide initial pain control. The time from initial pain control to the first supplementary dose in the surgical ward was significantly different (P less than 0.01) in the methadone group (20.7 +/- 20.2 h) when compared to the morphine group (6.2 +/- 3.0 h). Further, patients required significantly less (P less than 0.001) methadone (11.5 +/- 8.5 mg) than morphine (41 +/- 14.1 mg) in the surgical ward to provide adequate pain relief throughout the duration of the study (i.e., 60 h). There was a significant difference in visual analogue pain scores between the methoadone and morphine groups on postoperative days 1 and 2, suggesting the quality of pain relief was similar for both treatment groups. Blood opioid-concentration monitoring indicated that there was a relationship between blood opioid concentration and pain relief.(ABSTRACT TRUNCATED AT 250 WORDS)