Intradural morphine and diamorphine. Dose response studies.

This open study of 81 patients having major orthopaedic surgery reviews the duration of analgesia and side-effects of 0.625, 1.25 or 2.5 mg of morphine or 1.25 or 2.5 mg of diamorphine given intradurally in combination with 7.5 mg of cinchocaine at induction of anaesthesia. A significant dose-response relationship for duration of analgesia measured by time to first requirement of postoperative analgesic was found with morphine; 1.25 and 2.5 mg of morphine produced analgesia of longer duration than 0.625 mg. No such dose-response was found for side-effects. There was no significant difference in duration of analgesia between diamorphine 1.25 and 2.5 mg, and the duration was similar to that seen with the higher doses of morphine. An intradural dose of between 0.625 mg and 1.25 mg of either morphine or diamorphine used with cinchocaine and without additional parenteral opiate, may be appropriate.