Addition of oral clonidine to postoperative patient-controlled analgesia with i.v. morphine

Using a randomized, double-blind, placebo-controlled design, we have investigated, in 40 patients undergoing major abdominal surgery, the effect of oral clonidine 300 micrograms, 1 h before and 12 h after surgery on postoperative morphine requirements (evaluated by PCA). During the 24 h of the study, pain scores measured every 6 h did not differ significantly. Morphine requirements tended to be reduced in the clonidine group but the difference was not significant. There were no significant differences also in mean arterial pressure, ventilatory frequency and the incidence of pruritus and nausea. Heart rate was significantly lower until 18 h after surgery and sedation was significantly more pronounced in patients receiving clonidine. We cannot recommend routine oral administration of clonidine before surgery to improve postoperative analgesia.