674 MAINTENANCE OF EFFECT OF DULOXETINE IN PATIENTS WITH CHRONIC LOW BACK PAIN

The effect of journal impact factor, reporting conflicts, and reporting funding sources, on standardized effect sizes in back pain trials: a systematic review and meta-regression

BACKGROUND

Low back pain is a common and costly health complaint for which there are several moderately effective treatments. In some fields there is evidence that funder and financial conflicts are associated with trial outcomes. It is not clear whether effect sizes in back pain trials relate to journal impact factor, reporting conflicts of interest, or reporting funding.

METHODS

We performed a systematic review of English-language papers reporting randomised controlled trials of treatments for non-specific low back pain, published between 2006-2012. We modelled the relationship using 5-year journal impact factor, and categories of reported of conflicts of interest, and categories of reported funding (reported none and reported some, compared to not reporting these) using meta-regression, adjusting for sample size, and publication year. We also considered whether impact factor could be predicted by the direction of outcome, or trial sample size.

RESULTS

We could abstract data to calculate effect size in 99 of 146 trials that met our inclusion criteria. Effect size is not associated with impact factor, reporting of funding source, or reporting of conflicts of interest. However, explicitly reporting 'no trial funding' is strongly associated with larger absolute values of effect size (adjusted β=1.02 (95 % CI 0.44 to 1.59), P=0.001). Impact factor increases by 0.008 (0.004 to 0.012) per unit increase in trial sample size (P<0.001), but does not differ by reported direction of the LBP trial outcome (P=0.270).

CONCLUSIONS

The absence of associations between effect size and impact factor, reporting sources of funding, and conflicts of interest reflects positively on research and publisher conduct in the field. Strong evidence of a large association between absolute magnitude of effect size and explicit reporting of 'no funding' suggests authors of unfunded trials are likely to report larger effect sizes, notwithstanding direction. This could relate in part to quality, resources, and/or how pragmatic a trial is.

Duloxetine versus placebo in patients with chronic low back pain: a 12-week, fixed-dose, randomized, double-blind trial

This randomized, double-blind, placebo-controlled study assessed efficacy and safety of duloxetine in patients with chronic low back pain (CLBP). Adults (n = 401) with a nonneuropathic CLBP and average pain intensity of ≥ 4 on an 11-point numerical scale (Brief Pain Inventory [BPI]) were treated with either duloxetine 60 mg once daily or placebo for 12 weeks. The primary measure was BPI average pain. Secondary endpoints included Patient's Global Impressions of Improvement (PGI-I), Roland Morris Disability Questionnaire (RMDQ-24), BPI-Severity (BPI-S), BPI-Interference (BPI-I), and response rates (either ≥ 30% or ≥ 50% BPI average pain reduction at endpoint). Health outcomes included Short Form-36, European Quality of Life-5 Dimensions, and the Work Productivity and Activity Impairment questionnaire. Safety and tolerability were assessed. Compared with placebo-treated patients, duloxetine-treated patients reported a significantly greater reduction in BPI average pain (P ≤ .001). Similarly, duloxetine-treated patients reported significantly greater improvements in PGI-I, BPI-S, BPI-I, 50% response rates, and some health outcomes. The RMDQ and 30% response rate showed numerical improvements with duloxetine treatment. Significantly more patients in the duloxetine group (15.2%) than patients in the placebo group (5.4%) discontinued because of adverse events (P = .002). Nausea and dry mouth were the most common treatment-emergent adverse events with rates significantly higher in duloxetine-treated patients.

PERSPECTIVE

This study provides clinical evidence of the efficacy and safety of duloxetine at a fixed dose of 60 mg once daily in the treatment of chronic low back pain (CLBP). As of December 2009, duloxetine has not received regulatory approval for the treatment of CLBP.