A randomized double-blind comparison of a morphine-fentanyl combination vs. morphine alone for patient-controlled analgesia following bowel surgery.

An ideal patient-controlled analgesia (PCA) opioid would have both a rapid onset and a long duration of action, attributes, which are not available in currently existing opioids including morphine, the most widely used agent. A mixture of rapid onset and long-acting opioids may potentially achieve both these qualities. In a randomized, double-blind study, we compared a fentanyl-morphine combination with morphine alone for PCA, in 54 patients undergoing bowel surgery. The combination solution was prepared according to a 1:75 fentanyl to morphine potency ratio. The mixture contained fentanyl 13.33 mug/mL and morphine 1 mg/mL. The morphine alone solution contained 2 mg/mL. Patients were randomly allocated to one of the regimens and were then evaluated 4 times during the first 48 hours following surgery. Time to effect, visual analog pain scores, opioid consumption, demands, deliveries, and side effects on an opioid-related symptom distress scale were recorded. Groups were well matched for age, weight, and sex. There were no significant differences between groups in time to effect, PCA usage, pain scores or side effects other than the occurrence of nausea, which was lower for the combination group in 1 visit. Further studies are needed to explore the potential of different potency ratios and opioid combinations to achieve rapid and long-lasting pain control.