A double-blind comparison between epidural morphine and epidural clonidine in patients with chronic non-cancer pain

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Abstract
In a randomised double-blind study of 20 patients with chronic pain, epidural morphine 5 mg in 5 ml of saline was compared with epidural clonidine 150 .mu.g in 5 ml of saline. Thirteen patients had a clinical and radiological diagnosis of arachnoiditis, 6 had low back pain and 1 had post-operative scar pain. There was 18 females and 2 males with an average age of 52 years, range 22-76 years. There was no difference found between the 2 solutions in the resultant analgesia measured by the visual analogue scale for pain, pain relief or the pain word score during the 3 h period of the study. No difference was found in the patient''s mood which was also measured with the visual analogue scale. Two patients had no analgesia from either injection, 2 patients did not obtain any relief from clonidine and another 2 obtained no relief from morphine. Six patients reported that clonidine was better than morphine, 5 reported that morphine and clonidine were the same and 3 reported that morphine was better than clonidine. The duration of analgesia from the clonidine varied from 6 h to 1 month; the duration of analgesia from morphine varied from 6 to 24 h. Clonidine was associated with sedation and a fall in blood pressure of greater than 20 mm Hg in all patients, 1 patient required ephedrine to treat hypotension. Twelve patients had pruritus, 7 nausea and 2 vomiting following the morphine. Statistically there was no difference found between morphine and clonidine for short-term (3 h) analgesia in these patients. The duration of analgesia from clonidine in 2 patients was about 1 month while that from morphine did not exceed 24 h. The side effects from clonidine were less than those for morphine. This group of patients was unable to differentiate epidural morphine and clonidine for short-term analgesia. Further evidence of the importance of the spinal noradrenergic system in the transmission and treatment of patients with chronic pain.