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

BACKGROUND: 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). OBJECTIVES: The goal of this study was to determine whether efficacy of SMRs is associated with age, sex, or baseline LBP severity. METHODS: 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. RESULTS: 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). CONCLUSIONS: 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.

Predicting the Transition to Chronic Pain 6 Months After an Emergency Department Visit for Acute Pain: A Prospective Cohort Study.

BACKGROUND: Acute pain can transition to chronic pain, a potentially debilitating illness. OBJECTIVE: We determined how often acute pain transitions to chronic pain among patients in the emergency department (ED) and whether persistent pain 1 week after the ED visit was associated with chronic pain. METHODS: An observational cohort study conducted in two EDs. We included adults with acute pain (≤10 days) if an oral opioid was prescribed. Exclusion criteria were recent opioid use and use of any analgesics regularly prior to onset of the pain. Research associates interviewed patients during the ED visit and 1 week and 6 months later. The primary outcome, chronic pain, was defined as pain on > 50% of days since ED discharge. We constructed logistic regression models to evaluate the association between persistent pain 1 week after an ED visit and chronic pain, while adjusting for demographic and treatment variables. RESULTS: During a 9-month period, we approached 733 patients for participation and enrolled 484; 450 of 484 (93%) provided 1-week outcomes data and 410 of 484 (85%) provided 6-month outcomes data. One week after the ED visit, 348 of 453 (77%; 95% confidence interval [CI] 73-80%) patients reported pain in the affected area. New-onset chronic pain at 6 months was reported by 110 of 408 (27%; 95% CI 23-31%) patients. Presence of pain 1 week after ED visit was associated with chronic pain (odds ratio 3.6; 95% CI 1.6-8.5). CONCLUSIONS: About one-quarter of ED patients with acute pain transition to chronic pain within 6 months. Persistence of pain 1 week after the ED visit can identify patients at risk of transition.