Efficacy and safety of 40 mg or 60 mg duloxetine in Japanese adults with diabetic neuropathic pain: Results from a randomized, 52-week, open-label study

Introduction: To examine the long-term efficacy and safety of duloxetine in the treatment of Japanese patients with diabetic neuropathic pain, we carried out a 52-week, randomized, open-label extension of a 12-week, double-blind, placebo-controlled study. Materials and Methods: Japanese adults with diabetic neuropathic pain who completed the double-blind study were eligible for this long-term study, carried out at 71 sites in Japan (March 2008 to March 2010). Participants (n = 258) were re-randomized (1: 1) to 40 mg/day or 60 mg/day duloxetine. Pain (Brief Pain Inventory severity and interference), quality of life (Patient's Global Impression of Improvement), and safety (primary outcome; adverse events, vital signs, metabolic measures) were measured. Results: Significant (P < 0.0001) and sustained improvements (change +/- standard deviation; n = 257) were observed in Brief Pain Inventory severity (average pain score - 2.1 +/- 1.7). Improvements were also seen in Brief Pain Inventory interference (mean of subscores -0.96 +/- 1.52) and Patient's Global Impression of Improvement (-0.9 +/- 1.1) scores; these scores decreased significantly (P < 0.0001) during the long-term study. Frequently reported adverse events included somnolence (13.6%), constipation (13.2%) and nausea (10.5%). Increases were observed in plasma glucose, glycosylated hemoglobin and total cholesterol levels, and in bodyweight and heart rate; however, none of these were clinically meaningful. Overall, there were no clinically significant safety concerns. Conclusions: This is the first publication of a long-term study carried out in Asia with an entirely Japanese patient population to suggest that long-term duloxetine therapy for diabetic neuropathic pain is effective and has an acceptable safety profile..