History of depressive and/or anxiety disorders as a predictor of treatment response: A post hoc analysis of a 12-week, randomized, double-blind, placebo-controlled trial of paroxetine controlled release in patients with fibromyalgia

Background: Despite of a high comorbidity of depressive and/or anxiety disorders with fibromyalgia, information on the clinical implications of this comorbidity is limited but antidepressants are commonly prescribed to treat fibromyalgia in clinical practice. We investigated whether a history of depressive and/or anxiety disorders was associated with response to paroxetine controlled release (CR) in the treatment of fibromyalgia. Methods: One hundred sixteen (116) fibromyalgia subjects were randomized to receive paroxetine CR or placebo for 12 weeks. The primary outcome was treatment response defined as ≥ 25% reduction in the Fibromyalgia Impact Questionnaire (FIQ) score. In multivariate logistic regression, we determined if a history of depression and/or anxiety disorders was an independent predictor of response to paroxetine CR. Results: In logistic regression, the history of depression and/or anxiety did not predict treatment response as measured by ≥ 25% reduction in Fibromyalgia Impact Questionnaire (FIQ) score (OR = 0.66, 95% CI = .29-1.49, Wald = 0.97, p = 0.32), while the drug status (paroxetine CR) was significantly associated with treatment response (OR = 2.57, CI = 1.2-5.61, Wald = 5.5, p = 0.02). Conclusion: A significant proportion of patients with fibromyalgia had a history of anxiety and or depressive disorders. However response to treatment of fibromyalgia symptoms with paroxetine CR was not associated with a history of depressive and/or anxiety disorders. Our findings need to be confirmed in more adequately-powered and well-designed subsequent studies.