Background/Purpose: Patients with fibromyalgia (FM) usually experience pain, fatigue, and other debilitating symptoms for years. In clinical studies ranging from 3 months to >3 years, treatment with milnacipran was found to improve these symptoms. A post hoc analysis of milnacipran study data was conducted to examine whether duration of FM symptoms affected treatment outcomes.

Methods: Data were pooled from 2 double-blind trials that included patients randomized to milnacipran 100 or 200 mg/day (n=1311) or placebo (n=910). Outcomes were assessed in patients categorized into subgroups based on duration of FM symptoms at study baseline. Outcomes included percentage of patients with pain response (≥30% improvement in visual analog scale [VAS] recall pain scores) and composite response (≥30% pain improvement plus Patient Global Impression of Change score ≤2), as well as mean changes from baseline in VAS pain, Multidimensional Fatigue Inventory (MFI), Fibromyalgia Impact Questionnaire (FIQ), and Beck Depression Inventory (BDI) scores. Analyses were conducted using descriptive statistics.

Results: The mean duration of FM symptoms at baseline was 10.2 years (range = ≤3 month to 55 years); 33% of patients had experienced symptoms for <5 years and 10.4% for >20 years. Baseline pain, FIQ, and MFI were similar across the range of symptom durations; BDI scores were slightly higher in patients with shorter (1-2 years) symptom duration. Examination of treatment response trends across symptom duration subgroups indicated that the placebo responses were remarkably similar, regardless of treatment duration. Consistent with the percentage of composite responders observed in FM duration subgroups (Figure), improvements in pain, FIQ, MFI, and BDI were generally greater with milnacipran versus placebo across symptom durations >1 year. The milnacipran response was generally smaller for pain, FIQ, MFI, and BDI for patients with very short symptom durations (≤1 year) when compared with patients in other symptom duration subgroups.

Conclusion: Baseline levels of pain and other FM symptoms appeared to be largely independent of symptom duration. Treatment effects with milnacipran were relatively consistent across symptom duration for all symptom domains except for an unexplained smaller treatment effect size in patients with symptoms of shorter duration.