Effect of combining tramadol and morphine in adult surgical patients: a systematic review and meta-analysis of randomized trials

The role for tramadol in multimodal postsurgical analgesic strategies remains unclear. We undertook a systematic review to evaluate the utility of combining tramadol with morphine after surgery. We searched the MEDLINE, EMBASE, LILAC, Cochrane, and Clinical Trial Register databases for randomized, controlled studies comparing tramadol with placebo or active control in patients undergoing surgery. Fourteen studies (713 patients) were included. There was a limited but significant postoperative morphine-sparing effect, with a weighted mean difference (WMD) of −6.9 (95% confidence interval −11.3 to −2.5) mg. This effect was not associated with a decrease in morphine-related adverse effects. No difference in the incidence of nausea, vomiting, sedation, or shivering was observed. There was no decrease in pain intensity at 24 h; the WMD was −0.9 (−7.2; 5.2) on a 100 mm visual analogue scale at 24 h. We found no significant clinical benefit from the combination of i.v. tramadol and morphine after surgery.