The limited efficacy of tramadol in postoperative patients: a study of ED80 using the continual reassessment method

The aim of this study was to reevaluate the efficacy of tramadol for postoperative analgesia and to determine its ED80 (the clinical dose for which 80% of the patients had their pain adequately relieved) using the Continual Reassessment Method. Because the preliminary results of the first 24 patients were contradictory to the literature, we performed a second trial to verify and validate our data.

The study was double-blind and prospective. Participants were allocated to a dose of tramadol by 3-patient cohorts, in order of inclusion. The dose of tramadol received in each cohort was determined by the reaction of all previous patients. Five doses were chosen before beginning, with a probability of a positive reaction associated with each: 60 (0.4), 100 (0.55), 140 (0.7), 190 (0.8), and 260 mg (0.9). Tramadol was considered effective if the numeric pain scale was > or = 3/10 at T30.

The effective dose in 80% of patients was 260 mg for both trials. The probability of success of the 260 mg dose was 0.699 (95% credibility interval, 0.471-0.874) and 0.657 (95% credibility interval, 0.437-0.853) for trial 1 and trial 2, respectively.

Tramadol used as a sole drug cannot be considered the drug of choice after moderately painful surgery. The doses needed to relieve pain in 80% of patients are much larger than the usual dose of 100 mg. The Continual Reassessment Method allowed us to determine the ED80 of tramadol with a limited number of patients.