Open Access Highly Accessed Research article

Effect of duloxetine in patients with fibromyalgia: tiredness subgroups

Laurence A Bradley1, Robert Bennett2, Irwin J Russell3, Madelaine M Wohlreich4*, Amy S Chappell56, Fujun Wang7, Deborah N D'Souza8 and Harvey Moldofsky9

Author Affiliations

1 Division of Clinical Immunology and Rheumatology, University of Alabama at Birmingham, 177A Shelby Interdisciplinary Research Building, 1825 University Boulevard, Birmingham, Alabama 35294, USA

2 Oregon Health & Science University, 3455 SW US Veterans Hospital Road, Portland, OR 97239, USA

3 The University of Texas Health Science Center at San Antonio, 7703 Floyd Curl Drive, San Antonio, TX 78229, USA

4 Lilly Research Laboratories, Lilly Corporate Center, Indianapolis, IN 46285, USA

5 Medical, Neuroscience, Lilly Research Laboratories, Lilly Corporate Center, Indianapolis, IN 46285, USA

6 IU The Indiana University Medical Center, Department of Neurology, 545 Barnhill Drive, Indianapolis, IN 46202, USA

7 Statistics, Neuroscience, Lilly Research Laboratories, Lilly Corporate Center, Indianapolis, IN 46285, USA

8 Scientific Communications, Lilly Research Laboratories, Lilly Corporate Center, Indianapolis, IN 46285, USA

9 The Toronto Psychiatric Research Foundation, 951 Wilson Avenue, Toronto, Ontario, M3K 2S7, Canada

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Arthritis Research & Therapy 2010, 12:R141  doi:10.1186/ar3081

Published: 14 July 2010

Abstract

Introduction

This study tested the hypothesis that baseline ratings of fatigue/tiredness would be negatively associated with the efficacy of duloxetine on measures of pain and functional ability in patients with fibromyalgia.

Methods

A post hoc analysis of pooled data from 4 double-blind, placebo-controlled studies of duloxetine in fibromyalgia was performed. The fibromyalgia impact questionnaire (FIQ) tiredness item score (0 to 10 scale) was used to define tiredness subgroups. Patients were stratified into 3 subgroups: mild (0 to 3), moderate (4 to 6), and severe (7 to 10) tiredness. Analysis of covariance models and logistic regressions were used to test treatment-by-tiredness subgroup interactions.

Results

Data from the first 3 months are included in this post hoc analysis (duloxetine N = 797, placebo N = 535). At baseline, the distribution of tiredness severity in the duloxetine and placebo groups respectively was 3.64% and 3.75% mild, 16.71% and 15.57% moderate, and 79.65% and 80.68% severe. Rates of clinically significant (≥30% and ≥50%) improvement in brief pain inventory (BPI) average pain were similar across the tiredness subgroups. Tiredness severity at baseline was not negatively associated with the effects of duloxetine on patients' reports of functional ability using the FIQ total score, FIQ measures of physical impairment, interference with work, pain, stiffness, and depression and the medical outcomes study short form-36 (SF-36).

Conclusions

Studies of duloxetine in fibromyalgia have demonstrated clinically significant improvements in pain and functional ability (FIQ, SF-36). This post hoc analysis of data shows that the efficacy of duloxetine among patients with fibromyalgia does not vary as a function of baseline ratings of fatigue/tiredness.