Can the addition of clonidine improve the analgesic efficacy of low dose intrathecal morphine?: A randomised double-blind trial

Objective. To evaluate the influence of intrathecal clonidine on spinal morphine analgesia and adverse effects after major orthopaedic surgery. Methods. The study was approved by the local Ethics Committee. After written informed consent,45 ASA I-III patients scheduled for hip or knee replacement were included. Patients were randomly allocated to receive either placebo, 0.1 mg morphine or 0.1 mg morphine + 50 mug clonidine in addition to 15 mg bupivacaine intrathecally. The primary outcome parameter was the time to first opioid request. Statistical differences were calculated with U-test or Fisher's exact test. Results. Clonidine did not result in a significant improvement of postoperative analgesia. The mean time until first opioid request was for placebo 10.3 +/- 7.9 h, for 0.1 mg morphine 23.0 +/- 3.9 h and for 0.1 mg morphine + 50 mug clonicline 21 +/- 6.9 h, respectively. Clonidine significantly increased the rate of adverse effects. Conclusion. Our trial did not confirm an improved analgesia with the combination of intrathecal morphine and clonicline. Due to increased adverse effects the combination of intrathecal clonicline and morphine does not seem to be a reasonable alternative in the management of postoperative pain after orthopaedic surgery.