Background: Clonidine is an 2 adrenoreceptor and imidazoline receptor agonist which has analgesic, sedative and MAC sparing effects. It has been used orally, intravenously (including as an additive to morphine in PCA devices) and epidurally in combination with local anaesthetics and alone. We hypothesised that epidural administration of clonidine without local anaesthesia might provide adequate postoperative analgesia following spinal surgery without centroneuraxial block, and that if the drug’s effect site is spinal then this might be achieved with smaller doses and with fewer side effects than if given systemically.

Method: This randomised controlled trial evaluated the effect of epidural clonidine versus saline on analgesia requirement and pain scores following spinal decompressive surgery. 66 patients were recruited and received a standardized general anaesthetic. At the end of surgery group C received a bolus of 1.5 mcg/kg of epidural clonidine followed by an infusion of 25 mcg/h for 36 to 48 hours. Patients in group P received a similar bolus and infusion of saline. Verbal pain scores, morphine consumption by patient-controlled device (PCA), sedation score, haemodynamic variables and the incidence of PONV were recorded for up to 48 hours.

Results: Pain scores in both groups were low, but significantly lower for the first 6 hours in the clonidine group. Cumulative morphine consumption, used as a proxy for pain perception, was significantly lower in the morphine group throughout the whole period; mean (SEM) at 48 hours 62 (7) mg vs 35 (7) mg.

Conclusion: Epidural clonidine has a useful effect in post operative pain relief following spinal surgery with few side effects.