Results of a large systematic review and meta-analysis of randomized controlled trials show very “low certainty evidence” that non-benzodiazepine antispasmodics provide meaningful improvement in pain intensity in patients with low back pain – and may actually increase adverse event risk.
“We found that muscle relaxants might reduce pain in the short term, but on average, the effect is probably too small to be important, and most patients wouldn’t be able to feel any difference in their pain compared to taking a placebo,” study investigator Aidan Cashin, PhD, with the Center for Pain IMPACT, Neuroscience Research Australia, and University of New South Wales, Sydney, told this news organization. “There is also an increased risk of side effects,” he added.
The study was published online July 7 in The BMJ.
Global problem
Low back pain is a major global public health problem that burdens individuals, health care systems, and societies.
“Most people, around 80%, will have at least one episode of low back pain during their life,” Dr. Cashin noted.
Muscle relaxants, a broad class of drugs that include non-benzodiazepine antispasmodics and antispastics, are often prescribed for low back pain. In 2020 alone, prescriptions exceeded 1.3 million in England and topped 30 million in the United States.
“However, clinical practice guidelines have provided conflicting recommendations for the use of muscle relaxants to treat low back pain,” Dr. Cashin said.
To assess the efficacy and safety of muscle relaxants, the researchers conducted a detailed analysis of 31 randomized controlled trials that compared muscle relaxants with placebo, usual care, or no treatment in a total of 6,505 adults with nonspecific low back pain.
For acute low back pain, they found “very low certainty evidence” that non-benzodiazepine antispasmodics might reduce pain intensity at 2 weeks or less, but the effect is small – less than 8 points on a 0 to 100 point scale – and not clinically meaningful.
They found little to no effect of non-benzodiazepine antispasmodics on pain intensity at 3 to 13 weeks or on disability at any follow-up time points. None of the trials assessed the effect of muscle relaxants on long-term outcomes.
There was also low-certainty and very-low-certainty evidence that non-benzodiazepine antispasmodics might increase the risk of an adverse event, commonly dizziness, drowsiness, headache, and nausea (relative risk 1.6; 95% confidence interval, 1.2-2.0).
Better research needed
“We were surprised by the findings, as earlier research suggested that muscle relaxants did reduce pain intensity. But when we included all of the most up-to-date research, the results became much less certain,” said Dr. Cashin.
“We were also surprised to see that so much of the research wasn’t done very well, which means that we can’t be very certain in the results. There is a clear need to improve how research is done for low back pain so that we better understand whether medicines can help people or not,” Dr. Cashin said.
“We would encourage clinicians to discuss this uncertainty in the efficacy and safety of muscle relaxants with patients, sharing information about the possibility for a worthwhile benefit in pain reduction but increased risk of experiencing a nonserious adverse event, to allow them to make informed treatment decisions,” corresponding author James McAuley, PhD, University of New South Wales, said in an interview.
“We know that no matter what medicines people with low back pain are taking, they should avoid staying in bed, and they should try to be active and continue with their usual activities, including work, as much as they can. High-quality research shows that people who do this are more likely to recover faster and more completely,” said Dr. McAuley.
A symptom, not a diagnosis
Reached for comment, Andrew Hecht, MD, chief of spine surgery at Mount Sinai Health System, New York, noted that acute low back pain is “a symptom, not a diagnosis, and most episodes of acute low back pain without leg pain will resolve within a few weeks no matter what you do.”
“For people who have an episode of acute low back pain, we typically use anti-inflammatory medications, combined with a short, low dose course of a muscle relaxant if necessary, depending on the severity of symptoms, to help get you over the worst part of it,” Dr. Hecht said.
“We are trying to help the patient feel better in the short term and get more physically strong with therapy to try to reduce the frequency of these attacks in the future,” he added.
“But each patient is different. It’s not one-size-fits-all, and we don’t give prolonged courses of muscle relaxants because they have some side effects, like sedation,” Dr. Hecht cautioned.
The study had no specific funding. Dr. Cashin, Dr. McAuley, and Dr. Hecht have disclosed no relevant financial relationships.
A version of this article first appeared on Medscape.com.