Maintenance of effect of duloxetine in Chinese patients with pain due to osteoarthritis: 13-week open-label extension data

Abstract Background The objectives of this study were to assess the maintenance of effect of duloxetine 60 mg once-daily (QD) in Chinese patients with chronic pain due to osteoarthritis (OA) of the knee or hip and to provide additional long-term safety data. Methods This was an open-label, extension phase of a randomized, double-blind, placebo-controlled clinical trial. Eligible patients were outpatients who met the American College of Rheumatology clinical and radiographic criteria for OA with a rating ≥4 on Brief Pain Inventory (BPI) 24-h average pain. After completing the 13-week placebo-controlled phase, patients originally assigned to placebo were titrated to duloxetine 60 mg QD (PLA_DLX), whereas patients originally assigned to duloxetine 60 mg QD remained on the same dose of duloxetine (DLX_DLX) for another 13 weeks. The maintenance effect of duloxetine 60 mg QD during the extension phase was evaluated by a 1-sided 97.5% confidence interval (CI) of the baseline-to-endpoint change in the extension phase for patients who took duloxetine and reported ≥30% reduction in BPI average pain at the end of placebo-controlled phase (placebo-controlled phase duloxetine responders). Other BPI severity and interference items, as well as safety and tolerability, were assessed. Results Of 342 patients entering the extension phase, 162 (97.6%) DLX_DLX-treated patients and 157 (89.2%) PLA_DLX-treated patients completed this phase. Most patients (76.0%) were female. Mean age was 60.6 years. Mean BPI average pain was 5.5 at baseline of the placebo-controlled phase. Among 113 placebo-controlled phase duloxetine responders, mean change in BPI average pain during the extension phase was − 0.59 (from 2.47 to 1.88); the upper bound of the 1-sided 97.5% CI was − 0.31 and less than the pre-specified non-inferiority margin of a 1.5-point increase (p