1. Very low certainty evidence exists suggesting that non-benzodiazepine antispasmodics for lower back pain can reduce pain intensity, but not reduce disability, within two weeks.
2. More placebo controlled trials with different drug classes and durations of follow-up are needed to determine the efficacy, acceptability, and safety of muscle relaxants for lower back pain.
Evidence Rating Level: 1 (Excellent)
Lower back pain not only contributes significantly to the burden of disability around the world, but it is also associated with a very high economic burden, costing the United States approximately 134.5 billion dollars in healthcare expenses for 2016. Although muscle relaxants are the 3rd most commonly prescribed drug for lower back pain, guidelines in different countries conflict with each other, such as the US recommending non-benzodiazepine antispasmodics specifically, Belgium recommending no muscle relaxants, and the UK not making a recommendation either way. A previous systematic review showed that muscle relaxants provided a clinically significant decrease in pain (mean of 21.3 points on a 100-point scale). However, this review did not encompass randomized controlled trials (RCTs) from clinical trial registries. Therefore, the current review examined RCTs across numerous search databases and clinical trial registries to determine muscle relaxants’ efficacy, acceptability, and safety.
Overall, the study found very low certainty evidence that non-benzodiazepine antispasmodics diminished pain intensity at 2 weeks follow-up, as well as low certainty evidence that there may be a greater risk of adverse events. However, no difference in reduction of disability or acceptability of the drug regimen was found. This review underlies the need for higher quality RCTs assessing many classes of muscle relaxants and follow-up durations, as the body of research was limited for conditions other than non-benzodiazepine antispasmodics with 2 weeks follow-up.
In-Depth [systematic review and meta-analysis]: This review included RCTs where the study population consisted of adults with non-specific lower back pain. Participants were randomized to a group receiving a dose of muscle relaxant or a group receiving usual care, a placebo, or no treatment. In some RCTs, comparison were made between patients receiving two different muscle relaxants versus just one. The outcomes assessed were reduction in pain intensity and disability scores (on 100-point scales), acceptability (number of participants withdrawing from treatment for any reason), adverse events, and tolerability (number of participants withdrawing due to adverse events). The determination of whether evidence was low or high certainty was made using the GRADE approach. Overall, 49 studies were included in the review, and 31 in the meta-analysis. The results showed with very low certainty that non-benzodiazepine antispasmodics were associated with diminished pain intensity scores on or before 2 weeks (mean difference -7.7, 95% CI -12.1 to -3.3). There was also very low certainty for a reduction in disability scores (-3.3, 95% CI -7.3 to 0.7). Between 3 and 13 weeks, there was moderate certainty that no reduction in pain was found (mean difference 0.6, 95% CI -4.5 to 5.7). As well, there was very low certainty for finding no difference in acceptability (relative risk 0.8, 95% CI 0.6-1.1). There was also low certainty evidence for increased risk in adverse events (RR 1.6, 95% CI 1.2-2.0). With regards to drug classes other than non-benzodiazepine antispasmodics, no differences in efficacy were found except for a reduction in disability for benzodiazepines between 3 and 13 weeks (mean difference -6.9, 95% CI -12.1 to -1.7, moderate certainty evidence), although this data came from only one RCT. In general, many of the findings were of low certainty, whether the results were statistically significant or insignificant, demonstrating the need for larger, placebo-controlled RCTs to help determine the efficacy of muscle relaxants for lower back pain.
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