Effect of premedication with controlled-release oral morphine on postoperative pain. A comparison with intramuscular morphine.

Thirty fit patients presenting for elective total hip replacement were randomly allocated to receive a premedication of 60 or 90 mg controlled-release oral morphine or 15 mg intramuscular morphine. Postoperative analgesia was assessed using on-demand intravenous pethidine supplementation requirements. In 15 patients free plasma morphine concentrations were measured. Both 60 and 90 mg controlled-release oral morphine led to a reduced pethidine requirement compared to the intramuscular group but the reduction was not statistically different.