The Relative Efficacy of Seven Skeletal Muscle Relaxants. An Analysis of Data From Randomized Studies

Low back pain (LBP) causes 2.6 million visits to U.S. emergency departments (EDs) annually. These patients are often treated with skeletal muscle relaxants (SMRs).

The goal of this study was to determine whether efficacy of SMRs is associated with age, sex, or baseline LBP severity.

This was a planned analysis of data from 4 randomized studies of patients with acute nonradicular LBP. Patients were enrolled during an ED visit and followed-up 1 week later. The primary outcome was improvement in the Roland-Morris Disability Questionnaire (RMDQ) between ED discharge and the 1-week follow-up. We compared the change in RMDQ among 8 groups: placebo, baclofen, metaxalone, tizanidine, diazepam, orphenadrine, methocarbamol, and cyclobenzaprine. All patients also received a nonsteroidal anti-inflammatory drug. We performed analysis of variance to determine statistically significant differences between medications and linear regression to determine the association of age, sex, and baseline severity with the primary outcome.

The mean improvement in RMDQ per group was placebo 10.5 (95% confidence interval [CI] 9.5-11.5), baclofen 10.6 (95% CI 8.6-12.7), metaxalone 10.3 (95% CI 8.1-12.4), tizanidine 11.5 (95% CI 9.5-13.4), diazepam 11.1 (95% CI 9-13.2), orphenadrine 9.5 (95% CI 7.4-11.5), methocarbamol 8.1 (95% CI 6.1-10.1), and cyclobenzaprine 10.1 (95% CI 8.3-12). The between-group differences were not statistically significantly different. Results were similar regardless of age, sex, and baseline severity. Higher baseline RMDQ was associated with greater clinical improvement (B coefficient 5.7, p < 0.01). Adverse medication effects were more common with cyclobenzaprine than with placebo (p < 0.01).

Among patients in the ED with acute LBP treated with a nonsteroidal anti-inflammatory drug, SMRs do not improve outcomes more than placebo. Neither age, sex, nor baseline impairment impacts these results.