To investigate the efficacy of flexible dose duloxetine 60-120 mg/day on changes in fibromyalgia (FM) symptoms assessed by the Patient Global Impression of Improvement (PGI-I) scale.
Outpatients ≥ 18 years of age who met American College of Rheumatology criteria for FM, and had ≥ 4 score on the Brief Pain Inventory (BPI) average pain item, were randomized to duloxetine (n = 263) or placebo (n = 267) for 24 week double-blind treatment (primary endpoint at Week 12). Key secondary measures included BPI average pain severity, patient-rated scales assessing mood, anxiety, pain, sleep, and stiffness, Clinical Global Impression of Severity (CGI-S), Multidimensional Fatigue Inventory, Cognitive and Physical Functioning Questionnaire, Beck Depression Inventory (BDI), Beck Anxiety Inventory, and Medical Outcome Study Short-Form Health Survey (SF-36).
At Week 12, duloxetine-treated patients reported significantly greater global improvement with mean PGI-I scores of 2.8 compared to 3.4 in the placebo group (p < 0.001). Significantly more duloxetine- versus placebo-treated patients (57% vs 32%; p < 0.001) reported feeling "much" or "very much better" (PGI-I score ≤ 2). There was significantly greater improvement with duloxetine versus placebo treatment in BPI average pain severity, mood (including BDI total), anxiety (patient-rated only), stiffness, CGI-S, fatigue, all SF-36 domains (except role-physical and physical component summary), and being less bothered by pain or sleep difficulties. Treatment-emergent adverse events occurring significantly more frequently with duloxetine included: nausea, headache, constipation, dry mouth, dizziness, diarrhea, and hyperhidrosis.
Treatment with duloxetine 60, 90, and 120 mg/day was associated with feeling much better, pain reduction, being less bothered by sleep difficulties, and improvement in mood, stiffness, fatigue and functioning. (Clinical trial registry NCT00673452).