The Pharmacy and Therapeutics Committee at the authors’ institution reviewed the protocol for this study, and approval was obtained from the Research Ethics Board. The study began in July 2001, and the original goal was to recruit 50 patients. However, in July 2002 the study was interrupted by a labour disruption and was never resumed.
All women 21 years of age or older who were scheduled for abdominal hysterectomy during the study period and who met the inclusion and exclusion criteria were informed of the study, and all agreed to participate. During an interview at the preadmission clinic, a pharmacist (A.L.) informed each patient about the risks and benefits of the study and provided instructions on how to use the PCA device.Randomization was accomplished manually using a sealed-envelope system; unique numbers enclosed in the envelopes were used to generate the 2 groups, as described below. Of the original total of 50 envelopes prepared, 30 were distributed, 15 for each of the 2 treatment groups. Each patient was asked to select an envelope, and the enclosed number was used to assign the patient to receive either ketamine and morphine or morphine alone.
Ketamine has been added to morphine in previous studies, but there were no defined dosages for this combination. Therefore, the combination treatment consisted of a 1:1 mixture of ketamine 2 mg/mL and morphine 2 mg/mL; the morphine-only treatment consisted of a 2 mg/mL solution. Body mass index was calculated to account for any difference in volume of distribution for patients who received both morphine and ketamine. The concentrations chosen were different from those used in other similar studies. The treatments were to be delivered as postoperative PCA, via syringes prepared by pharmacy technicians. There was no wash-out period, no placebo group, no additional investigation or invasive procedures, and no permanent implantation of devices. Neither the patients nor the investigators were aware of the groups to which patients had been assigned.