Muscle relaxants: evidence review finds no support for use in low back pain

An Australian review has shown that muscle relaxants are unsuitable for low back pain treatment, providing little to no benefit and exposing patients to adverse events.

The study – published in the BMJ – reviewed 49 randomised controlled trials in adults with non-specific low back pain that assessed antispastics (eg baclofen), benzodiazepines, antispasmodics and miscellaneous drugs such as Botulinum toxin.

Meta-analysis of 31 trials revealed “very low certainty evidence” that non-benzodiazepine antispasmodics reduced acute low back pain intensity but the modest difference was unlikely to be clinically meaningful.

The drugs also failed to reduce disability and may increase adverse event risk.

No pain or disability benefits were seen in at three to 13 weeks.

The review also found that non-benzodiazepine antispasmodics could increase the risk of adverse events such as dizziness, drowsiness, headache, and nausea.

The study authors said muscle relaxants were still recommended in some international  guidelines for low back pain, but co-author Aidan Cashin, a doctoral student at the Centre for Pain IMPACT, Neuroscience Research Australia, Sydney, told the limbic muscle relaxants were prescribed at a relatively low rate in Australia.

“It is estimated that 3 out of 100 GP visits will result in a patient with low back pain being prescribed a benzodiazepine muscle relaxant,” he said.

“The prescription rate of non-benzodiazepine antispasmodic and antispastic muscle relaxants is less frequent.”

Internationally, however, muscle relaxants are “the third most commonly prescribed drug for low back pain”, the study authors said.

Current international guidelines have conflicting recommendations about muscle relaxants and low back pain.

“For example, of 15 clinical practice guidelines, six recommend muscle relaxants to manage low back pain, five do not recommend them, and four do not offer a recommendation,” Mr Cashin said.

“The most recent (2016) Australian clinical practice guideline by the NSW Agency for Clinical Innovation does not make a recommendation about the prescription of muscle relaxants for low back pain.”

Although earlier research suggested that muscle relaxants led to large reductions in pain intensity, the latest data is much less certain, Mr Cashin said.

“We were surprised to see that so much of the research wasn’t done very well, which means that we can’t be very certain of the results.”

Mr Cashin said future guidelines should consider this uncertainty when making recommendations around muscle relaxants and low back pain.

For now, he suggests clinicians talk to patients about the ambiguity around muscle relaxants’ risks and benefits so they can make informed treatment decisions, and encourage patients to “avoid staying in bed”, “try to be active, and continue with usual activities, including work, as much as they can”.

“The best quality research shows that people who do this are more likely to recover faster and more completely,” Mr Cashin said.

For muscle relaxants and low back pain, “large, high-quality, placebo controlled trials are urgently needed to resolve uncertainties about [their] efficacy and safety …”, the study concluded.

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