Little evidence exists to support antispasmodics for low back pain

For patients with low back pain, only very low- and low-certainty evidence shows that nonbenzodiazepine antispasmodics might provide small but not clinically important reductions in pain intensity, a systematic review found.

Researchers reviewed 31 randomized controlled trials including 6,505 patients that examined muscle relaxants compared with placebo, usual care, a waiting list, or no treatment in adults with nonspecific low back pain. Eighteen muscle relaxants, most commonly nonbenzodiazepine antispasmodics (n=29), miscellaneous (n=11), antispastics (n=5), and benzodiazepines (n=4), were investigated. Outcomes included pain intensity and disability on a scale of 0 to 100, acceptability based on discontinuation of the drug during treatment for any reason, and safety based on adverse events. Results were published by The BMJ on July 8.

The researchers found with very low certainty that nonbenzodiazepine antispasmodics were associated with reduced pain at two weeks or less, with a mean difference of −7.7 points (95% CI, −12.1 to −3.3 points); the reduction in disability was not significant, at a mean difference of −3.3 points (95% CI, −7.3 to 0.7 points). Low- and very low-certainty evidence indicated that nonbenzodiazepine antispasmodics might increase risk for an adverse event (relative risk, 1.6; 95% CI, 1.2 to 2.0) and might show little or no difference in acceptability (relative risk, 0.8; 95% CI, 0.6 to 1.1) versus controls.

The study authors noted that only a few trials investigated other muscle relaxants and different durations of low back pain and that certainty of evidence was reduced because most trials had high risk for bias. While nonbenzodiazepine antispasmodics might reduce pain intensity at two weeks or less, the drugs could increase the risk of dizziness, drowsiness, headache, and nausea. However, these effects might not make a patient stop taking medication, suggesting that the treatment could be acceptable, the authors wrote.

“Although the observed effect of non-benzodiazepine antispasmodics in reducing pain compared with control at two weeks or less was statistically significant, the magnitude of the effect was too small to be considered clinically important,” the authors wrote. “The upper limits of the confidence interval do not, however, exclude a clinically meaningful effect on pain intensity. The modest overall effect is reported at group level, which could still mean that some, but not all, individuals gain a worthwhile benefit.”