Little Evidence That Muscle Relaxants Work for Low Back Pain

(Reuters Health) – Muscle relaxants, despite being widely prescribed for patients with low back pain, are not very effective, a new study suggests.

A review and meta-analysis of 49 earlier studies found low-certainty evidence that non-benzodiazepine antispasmodics were associated with a small reduction in pain intensity but not a reduction in disability. Low- and very low-certainty evidence showed that the medications might increase the risk of an adverse event, according to the report published in The BMJ.

“Our research study shows that on average, muscle relaxants provide only a small, non-clinically important reduction in acute low back pain,” said lead author Aidan Cashin, a researcher at Neuroscience Research Australia and the University of New South Wales. “That being said, the research is mostly poor quality and some muscle relaxants, particularly non-benzodiazepine antispasmodic medicines, may improve pain for some people. Large, high quality research is urgently needed to resolve uncertainties around the efficacy and safety of these medicines for low back pain.”

These medications aren’t meant to cure low back pain, Cashin said in an email.

“For most people it is very difficult to know with any certainty what is causing low back pain, and therefore many treatments try to provide pain relief rather than try to fix what might be causing the pain,” he added. “Muscle relaxants are commonly prescribed to reduce pain, not to cure whatever is causing the pain.”

Regardless, it’s important to remind patients with low back pain that they shouldn’t take too much time off because of their painful backs, Cashin said. “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.”

The researchers note that muscle relaxants are frequently prescribed in the UK and the U.S., with prescriptions during 2020 exceeding 1.3 million in England and more than 30 million in the U.S.

To investigate the effectiveness and safety of muscle relaxants, Cashin and his colleagues qualitatively analyzed 31 studies sampling 6,505 participants.

Outcomes included pain intensity (measured on a 0-100 point scale), disability (0-100 point scale), acceptability and safety (adverse events, serious adverse events, and number of participants who withdrew from the trial because of an adverse event).

For acute low back pain, very low-certainty evidence showed that at two weeks or less non-benzodiazepine antispasmodics were associated with a reduction in pain intensity compared with control (mean difference −7.7) but not a reduction in disability (−3.3). Low- and very low-certainty evidence showed that non-benzodiazepine antispasmodics might increase the risk of an adverse event (relative risk 1.6) such as dizziness, drowsiness, headache and nausea, and might have little to no effect on acceptability compared with control for acute low back pain.

“This is definitely an important topic to investigate and think about,” said Dr. Eliana Cardozo, an assistant professor of rehabilitation medicine at the Icahn School of Medicine at Mount Sinai and a specialist in sports medicine at The Mount Sinai Hospital in New York City. “Muscle relaxants are used a great deal for low back pain. That said, I wasn’t surprised by the results of this review article. All of us who do prescribe these medications know they make people drowsy. I think the most important thing for the physician is to prescribe them in the correct context and for the right patient.”

One of those contexts is back pain at night that interferes with sleep, Dr. Cardoza said. “Then the issue of drowsiness isn’t an issue but actually a good thing,” she said. “Most colleagues I know don’t use them for pain during the day.”

Dr. Cardoza agrees that “it’s important to do larger and better-quality studies. It’s hard to take too much from this study. The studies they picked had many variables and they used different muscle relaxants so it’s hard to compare one to another. Some were using the medications for acute low back pain and others for chronic pain.”

SOURCE: The BMJ, online July 7, 2021.

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