Level 2: Mid-level evidence
The FDA has approved duloxetine (Cymbalta) to treat chronic musculoskeletal pain, including discomfort from osteoarthritis and chronic low-back pain. Several recent randomized trials have evaluated the efficacy of duloxetine for pain reduction in patients with chronic low-back pain, but the trials were of short duration (12-13 weeks) and had high dropout rates.
One trial randomized 401 adult patients to duloxetine 60 mg vs. placebo once daily for 12 weeks. Duloxetine was associated with significant improvement, with ≥50% pain reduction in 48.7% vs. 34.7% (P=0.006, NNT 8) ( J Pain. 2010;11:1282-1290). Another trial with 236 patients randomized to individually adjusted doses of duloxetine (60-120 mg) vs. placebo showed a nonsignificant trend toward greater pain reduction with duloxetine (≥50% pain reduction in 38.5% vs. 27%, P=0.09) (Spine [Phila Pa 1976]. 2010;35:E578-585).
In a third trial, 404 patients received duloxetine at one of three doses (20 mg, 60 mg or 120 mg) vs. placebo. There was no significant pain reduction for either the 20-mg or 60-mg duloxetine doses. At 120 mg (maximal approved dose), duloxetine was associated with more patients achieving ≥30% pain reduction (57.8% vs. 43.4%, P=0.033, NNT 7), but there was not a significant difference in ≥50% pain reduction (Eur J Neurol. 2009;16:1041-1048). In each trial, duloxetine was associated with increased risk of discontinuation due to adverse effects (NNH 6-12). All of the trials had high dropout rates (23%-34%).