Objectives: The aim of this study was to evaluate the opioid response in patients receiving morphine and pregabalin, independently from the presumed pain mechanisms, in comparison with patients receiving morphine treatment only.

Methods: A multicenter prospective randomized controlled study was carried out in a sample of 70 advanced cancer patients with pain requiring strong opioids. Thirty-five patients (group MO) were randomized to receive sustained-release morphine using initial doses of 60 mg/day. Thirty-five patients (group MO-PR) were randomized to start the same morphine doses and pregabalin in increasing doses, starting with 25 mg/day up to 150 mg/day in one week. The following data were also recorded before starting the treatments (T0) and then at week intervals for four weeks (W1-4): age, gender, primary cancer and known metastases, pain causes and mechanisms, symptoms associated with opioid therapy, pain intensity, Brief Pain Inventory (BPI), morphine doses and escalation indexes (OEIs), and quality of life.

Results: Forty-eight patients completed the study, twenty-eight and sixteen patients in group MO and MO-PR, respectively. Twenty patients were females, the mean age was 65.5 (± 10.3), and the mean Karnofsky status was 66.0 (± 18.9). No differences between groups were found in age (P = 0.839), Karnofsky status (P = 0.741), opioid doses as well as escalation indexes (OEI mg, P = 0.260, and OEI%, P = 0.270). No differences between the two groups were found in quality of life and all BPI items.

Conclusion: The use of low doses of pregabalin added to morphine therapy in advanced cancer patients does not seem to provide advantageous analgesic effects, despite limitations of the present study due to the number of drop-outs.