For 22 years, American Family Physician (the journal of the American Academy of Family Physicians) has been publishing an annual review of the top 20 research studies of interest to family physicians, identifying original research that is most likely to change and improve primary care practice and that represents POEMS (Patient Oriented Evidence that Matters). I was interested to read in the July 2021 issue that muscle relaxants are not reliably effective adjuncts for treating acute low back pain. The full text is available online.
Confusingly, that evidence was contradicted by another article in the same issue on Pharmacologic Therapy for Acute Pain that said “muscle relaxants may be useful for acute low back pain”. It gave a top A rating to the evidence, based on systematic review and multiple randomized controlled trials.
So which is it? Are muscle relaxants effective adjuncts for treating acute low back pain or not? They conveniently provided references for both statements, so I was able to go to the sources they relied on.
The evidence provided to support the “No” conclusion was a single study by Friedman et al. published in the Annals of Emergency Medicine in 2019. The title was “A Randomized, Placebo-Controlled Trial of Ibuprofen Plus Metaxalone, Tizanidine, or Baclofen for Acute Low Back Pain“. It found that “Adding baclofen, metaxalone, or tizanidine to ibuprofen does not appear to improve functioning or pain any more than placebo plus ibuprofen by 1 week after an ED visit for acute low back pain”.
A review on The NEJM Journal Watch called it a high quality study and commented that it was no surprise, since it corroborated previous studies showing a lack of evidence for the effectiveness of muscle relaxants for this condition. In another study, diazepam (another drug commonly used as a muscle relaxant) was also no better than placebo.
The evidence provided to support the “Yes” conclusion consisted of twice as many references, but only two studies. One of the studies must be disregarded because it was not actually a study and was only a clinical practice guideline for neck pain, not low back pain. The other was a Cochrane systematic review by van Tulder et al. It evaluated muscle relaxants alone and in various combinations with analgesics for acute low back pain. For muscle relaxants + analgesics vs. placebo + analgesics, it found six studies suitable for evaluation.
Of the six studies they identified for acute LBP, five were considered to be high quality (Berry 1988b; Corts Giner 1989; Hingorani 1966; Sirdalud 1998; Tervo 1976) and one was a low quality trial (Borenstein 1990). Five trials evaluated non‐benzodiazepines and only one trial benzodiazepines (Hingorani 1966). All are described in the Cochrane review. For some endpoints, there was no statistical difference; for others they found modest improvement. They questioned the clinical importance of the improvement. Overall, they claimed to have found “strong evidence that non‐benzodiazepines are effective for acute LBP”. You can read the results of each study on the Cochrane website and judge for yourself. They concluded that “Muscle relaxants are effective in the management of acute and chronic non‐specific low back pain, but the adverse effects (most often drowsiness and dizziness) require that they be used with caution”. They mentioned a Danish report that reached a negative conclusion, “Muscle relaxants, for example diazepam, should play no role in the treatment of back pain. The possible positive effects are greatly overshadowed by the risk of physical and psychological dependency, even after short term usage”. I queried PubMed and didn’t find the results very helpful.
Conclusion: Maybe yes, maybe no
I am disappointed that AFP provided mixed messages and less-than-impressive scientific evidence. I am left wondering whether adding muscle relaxants to analgesic treatment of acute low back pain is worthwhile. I am skeptical. In the absence of more convincing evidence, I would be hesitant to prescribe muscle relaxants for adjunct treatment.