The primary objectives of this study were to assess the efficacy and safety of duloxetine for reducing pain severity in fibromyalgia patients with or without current major depressive disorder. This was a 6-month, multicenter, randomized, double-blind, placebo-controlled study. In total, 520 patients meeting American College of Rheumatology criteria for fibromyalgia were randomly assigned to duloxetine (20 mg/day, 60 mg/day, or 120 mg/day) or placebo, administered once daily, for 6 months (after 3 months, the duloxetine 20-mg/day group titrated to 60 mg/day). The co-primary outcome measures were the Brief Pain Inventory (BPI) average pain severity score and Patient Global Impressions of Improvement (PGI-I) score. Safety was assessed via treatment-emergent adverse events, and changes in vital sign, laboratory, and ECG measures. Compared with placebo-treated patients, those patients treated with duloxetine 120 mg/day improved significantly more on the co-primary outcome measures at 3 months (change in BPI score [-2.31 vs -1.39, P<0.001] and PGI-I [2.89 vs 3.39, P=0.004]) and at 6 months (change in BPI [-2.26 vs -1.43, P=0.003] and PGI-I [2.93 vs 3.37, P=0.012]). Compared with placebo, treatment with duloxetine 60 mg/day also significantly improved the co-primary measures at 3 months and BPI at 6 months. Duloxetine was efficacious in patients both with and without major depressive disorder. There were no clinically significant differences between treatment groups in changes in vital signs, laboratory measures, or ECG measures. Study results demonstrated that duloxetine at doses of 60 mg/day and 120 mg/day appears to be safe and efficacious in patients with fibromyalgia.
Pain is a common cause of disability in osteoarthritis. Duloxetine, a serotonin and norepinephrine reuptake inhibitor (SNRI), has demonstrated analgesic effects in diabetic peripheral neuropathy and fibromyalgia. Considering its central mechanism of action, duloxetine may be effective in other pain states with evidence of central sensitization. Herein, we report the results of a 13-week, randomized, double-blind, placebo-controlled trial of duloxetine (60-120 mg/day) versus placebo in the treatment of knee pain in 231 patients meeting clinical and radiographic criteria for osteoarthritis of the knee. Duloxetine was superior to placebo on the primary efficacy measure (weekly mean 24-h pain scores) beginning at Week 1 and continuing through the treatment period (P < or = .05). There was also a significant improvement in the WOMAC physical functioning subscale and several other secondary outcomes. Adverse-event rates did not differ significantly between treatment groups (49.5% for duloxetine 60-120 mg/day, and 40.8% for placebo).
There has been an increase in the number of chronic pain clinical trials in which the treatments being evaluated did not differ significantly from placebo in the primary efficacy analyses despite previous research suggesting that efficacy could be expected. These findings could reflect a true lack of efficacy or methodological and other aspects of these trials that compromise the demonstration of efficacy. There is substantial variability among chronic pain clinical trials with respect to important research design considerations, and identifying and addressing any methodological weaknesses would enhance the likelihood of demonstrating the analgesic effects of new interventions. An IMMPACT consensus meeting was therefore convened to identify the critical research design considerations for confirmatory chronic pain trials and to make recommendations for their conduct. We present recommendations for the major components of confirmatory chronic pain clinical trials, including participant selection, trial phases and duration, treatment groups and dosing regimens, and types of trials. Increased attention to and research on the methodological aspects of confirmatory chronic pain clinical trials has the potential to enhance their assay sensitivity and ultimately provide more meaningful evaluations of treatments for chronic pain.
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