Comparison of tramadol with morphine for post-operative pain following abdominal surgery.

In a multi-centre, double-blind, randomized study involving 523 patients, the analgesic efficacy of tramadol was compared to that of morphine given in repeated intravenous boluses as required to control post-operative pain following abdominal surgery over 24 h. Intravenous administration of the study analgesic started as soon as the patient reported pain. Patients received an initial dose (either tramadol 100 mg or morphine 5 mg) and, if necessary, repeat doses of tramadol 50 mg or morphine 5 mg could be given on demand over the first 90 min. Further doses up to a total of tramadol 400 mg or morphine 40 mg could then be given after 90 min up to 24 h after the first dose of study medication. The primary efficacy parameter was the responder rate (no or slight pain) within the first 90 min of treatment. Whilst responder rates reached 72.6% with tramadol and 81.2% with morphine, the treatments were statistically equivalent and the observed difference in the responder rates between the groups was within the predefined range of +/- 10%. Mean cumulative doses received by treatment responders amounted to 188.2 mg within the first 1.5 h and 157.1 mg during the subsequent 22.5 h in the tramadol group and 13.9 and 18.4 mg, respectively, in the morphine group. A high incidence of gastrointestinal adverse events were observed with both treatments mostly consisting of mild nausea, dry mouth, vomiting, dyspepsia and hiccups.