Duloxetine 60 mg for chronic low back pain: post hoc responder analysis of double-blind, placebo-controlled trials

Abstract

Introduction

Duloxetine has demonstrated efficacy in chronic low back pain (CLBP). We examined the predictors of response to duloxetine for CLBP.

Patients and methods

This was a post hoc analysis of pooled data from 4 double-blind, ran-domized, placebo-controlled trials of duloxetine (60 mg/day for 12–14 weeks) in adult patients with CLBP. Primary outcome was proportion of patients with ≥30% reduction in Brief Pain Inventory (BPI) average pain (“pain reduction”) at 12–14 weeks. The proportion of patients with ≥30% and ≥50% (secondary outcome) pain reduction in duloxetine and placebo groups was compared. Variables for responder analyses were early improvement (≥15% pain reduction at Week 2), sex, age, baseline BPI average pain score, duration of CLBP, and number of painful body sites according to the Michigan Body Map (≥2 vs 1 [isolated CLBP]; 1 trial); relative risk (RR) and 95% confidence interval (CI) were calculated.

Results

Compared with placebo (n = 653), a greater proportion of duloxetine-treated patients (n = 642) achieved ≥30% (59.7% vs 47.8%; P < 0.001) and ≥50% pain reduction (48.6% vs 35.1%; P < 0.001). Among duloxetine-treated patients, early improvement was associated with greater likelihood of ≥30% (RR [95% CI], 2.91 [2.30–3.67]) or ≥50% (3.24 [2.44–4.31]) pain reduction. Women were slightly more likely than men to achieve ≥30% (RR [95% CI], 1.14 [1.00–1.30]) or ≥50% (1.17 [0.99–1.38]) pain reduction. Response rates were similar between age, CLBP duration, and baseline BPI average pain score subgroups. Patients with ≥2 painful sites were more likely to respond to duloxetine 60 mg relative to placebo than patients with isolated CLBP (RR, duloxetine vs placebo [95% CI]: ≥30% reduction, ≥2 painful sites 1.40 [1.18–1.66], isolated CLBP 1.07 [0.78–1.48]; ≥50% reduction, ≥2 painful sites 1.51 [1.20–1.89], isolated CLBP 1.23 [0.81–1.88]).

Conclusion

Early pain reduction was indicative of overall response. Patients with multiple painful sites had more benefit from duloxetine than patients with isolated CLBP.

Keywords:

• Brief Pain Inventory
• chronic pain
• SNRI
• low back pain
• Michigan Body Map
• multiple painful sites

Acknowledgments

The authors would like to thank all study participants and Dr Chad Brummet (University of Michigan), who provided the Michigan Body Map. Medical writing assistance was provided by Rebecca Lew, PhD, CMPP, and Mark Snape, MB BS, CMPP, of ProScribe – Envision Pharma Group, and was funded by Eli Lilly Japan K.K. ProScribe’s services complied with international guidelines for Good Publication Practice (GPP3). This study was sponsored by Eli Lilly Japan K.K., manufacturer and licensee of Cymbalta^® in Japan. The study NCT01855919 was conducted by Shionogi & Co. Ltd. and funded by Eli Lilly Japan K.K. and Shionogi & Co. Ltd.

Disclosure

SK has received consulting fees and honoraria from Eli Lilly Japan K.K. and Shionogi & Co. Ltd and has received research funding from Shionogi & Co. Ltd. LA, HE, SF, KO, and AY are employees of Eli Lilly Japan K.K. MI and TT are employees and minor stock holders of Shionogi & Co. Ltd. LA and SF hold shares in Eli Lilly and Company. The authors report no other conflicts of interest in this work.