Premedication with slow release morphine (MST) and adjuvants

Sixty-one women undergoing major gynaecological surgery received slow release morphine (MST) 60 mg, with placebo, hyoscine 0.6 mg or diazepam 10 mg, by mouth 2 h before surgery. Plasma morphine concentrations reached a steady level usually within 3 h after administration of MST, and did not increase after surgery unless supplementary opioid was given. Hyoscine delayed morphine absorption. Before operation no fewer than 50% of patients were sedated after MST alone, but this increased to 85% after MST and diazepam. Similarly, only the combination MST and diazepam produced anxiolysis. Postoperative mood was unhappier after MST and hyoscine. Emesis occurred in 40-57% of patients, and was not reduced by hyoscine. Therefore premedication with MST alone did not produce reliable sedation or anxiolysis. A combination of hyoscine and MST premedication cannot be recommended, as it did not produce sedation, anxiolysis or antiemesis and hyoscine may have delayed morphine absorption.