Influence of naloxone on the postoperative analgesic and respiratory effects of buprenorphine

Eighty patients recovering from major operations were investigated to evaluate the influence of naloxone on the analgesic and respiratory depressant properties of buprenorphine. They were randomly assigned to two groups to self-administer either buprenorphine (Group B) or a mixture of buprenorphine and naloxone (fraction 60%; Group BN) in the early postoperative period by means of the On-Demand Analgesia Computer (ODAC). The duration of patient-controlled analgesia (PCA) was 21.0 h (B) or 23.5 h (BN), during which 12.2 (B) and 18.2 (BN) demands per patient were recorded, representing significantly different consumption of buprenorphine 0.80 (B) and 1.07 (BN) µg·kg−1·h−1. Retrospective pain scores were significantly better in Group B, and respiratory rate was significantly higher in Group BN. The analgesia was judged superior by 81% (B) and 88% (BN) of the patients compared to conventional postoperative pain treatment. The minimum effective buprenorphine concentration (MEC) varied greatly in both groups with no significant differences between them (median 0.4 ng·ml−1, range 0.1–8.6 ng·ml−1); intra-individual variability was lower (67.9% B, and 58.2% BN) than inter-individual variability (107.3% B and 84.0% BN). Accumulation in plasma and acute tolerance did not occur. Thus, admixture of 60% naloxone decreased both the analgesic and respiratory depressant effects of buprenorphine which were generally independent of plasma concentrations. The analgesia achieved with the buprenorphine/naloxone mixture under patient-controlled conditions was comparable to that of other narcotic analgesics. Accordingly, this drug combination may be expected to give clinically adequate analgesia without notable impairement of spontaneous respiration, whilst withdrawal symptoms would probably arise in drug addicts abusing other opiates.