Muscle relaxants are largely ineffective for low back pain, although they are often prescribed for the condition, suggests an analysis of the latest findings published today by the BMJ.
The results show that while muscle relaxants can provide short-term pain relief, the effect is too small to be considered clinically meaningful and there is an increased risk of side effects.
However, the researchers stress that the certainty of evidence is low and say that large studies are urgently needed to remove the uncertainties about the use of these drugs for back pain.
Low back pain is a global public health problem, and muscle relaxants (a broad class of drugs that include non-benzodiazepine anticonvulsants and antispasmodics) are widely prescribed.
For example, in 2020 prescriptions exceeded 1.3 million in England and over 30 million in the US. Nevertheless, the guidelines of clinical practice around the world give contradicting recommendations for their application.
To address this, researchers in Australia looked at the effectiveness, acceptability, and safety of muscle relaxants versus placebo, usual treatment, or no treatment in adults with nonspecific lower back pain.
They reviewed and performed a detailed analysis of the evidence from 31 randomized controlled trials with over 6,500 participants published as of February 2021.
The quality of the studies varied, but the researchers were able to assess the certainty of evidence using the recognized GRADE system.
They identified a difference of at least 10 points on a scale of 0 to 100 for pain and disability as the smallest clinically meaningful effect – a threshold used in other studies on low back pain.
Evidence with very little certainty showed that anticonvulsant non-benzodiazepines can reduce pain intensity in patients with acute low back pain compared to controls after two weeks or less. However, this effect is small – less than 8 points on a 0-100 point scale – and does not meet the usual thresholds for being clinically relevant.
There was little to no effect of non-benzodiazepine spasmodics on pain intensity at 3-13 weeks or on disability at all follow-up times.
Low and very low certainty evidence also showed that non-benzodiazepine anticonvulsants increase the risk of adverse events (often dizziness, lightheadedness, headache, and nausea) and may have little to no effect on treatment discontinuation compared to controls .
No studies examined the effects of muscle relaxants on long-term outcomes.
Although this analysis was based on the best study evidence available, the researchers acknowledge some caveats, saying that the modest overall effect could still mean that some, but not all, people will get worthwhile benefits.
However, they emphasize that the low to very low level of certainty of evidence does not allow for clear recommendations.
“We encourage clinicians to discuss this uncertainty about the efficacy and safety of muscle relaxants with patients and to share information about the possibility of a worthwhile benefit in reducing pain but the increased risk of a non-serious adverse event, to enable them to to find out about treatment decisions, ”they write.
“Large, high-quality, placebo-controlled trials are urgently needed to resolve uncertainties about the effectiveness and safety of muscle relaxants for low back pain,” they conclude.
Cashin, AG, et al. (2021) Efficacy, Acceptance, and Safety of Muscle Relaxants for Adults with Nonspecific Low Back Pain: Systematic Review and Meta-Analysis. BMJ. doi.org/10.1136/bmj.n1446.