In this randomized, double blind placebo controlled study, the authors evaluated the effects of oral clonidine premedication on very low dose epidural morphine analgesia in 50 hysterectomy patients. Patients were randomized to receive a single oral clonidine 300 μg (n = 25) or a placebo (n = 25) 90 minutes before insertion of the epidural catheter. 3 ml of 2% lidocaine with adrenaline (5 μg ml-1) mixed with 2 mg morphine were injected via epidural, followed by an additional volume of 2% lidocaine with adrenaline (5 μg ml-1) titrated to T6 block height before commencing general anesthesia. The postoperative analgesia regimen was 2 mg of intravenous morphine every 10 minutes for the first 48 hr and 1 gm of oral acetaminophen every 4-6 hr after initiation of oral diet at 24-48 hr as required. Morphine consumption, acetaminophen, pain scores, and side effects were recorded thoughout 48 hr after surgery. The results show patients in the clonidine and placebo groups were not different in terms of local anesthetics dose (p = 0.27), total morphine and
acetaminophen requirement (p = 0.34, p = 0.1) respectively. Pain scores at rest and movement were also not different in both groups (p = 0.83, p = 0.64) respectively. No serious adverse effects were noted. The authors concluded that oral clonidine approximately 6 μg kg-1 does not enhance the analgesic effect of epidural morphine 2 mg after hysterectomy.

Keywords: Oral clonidine, Epidural morphine, Postoperative analgesia, Adverse effects, Total abdominal hysterectomy