An analysis of the evidence published in The BMJ finds that, despite nearly 60 years of research, there is still a lack of high certainty evidence on the effectiveness and safety of commonly used painkillers (analgesics) for short bouts of low back pain.
According to the researchers, “clinicians and patients are advised to take a cautious approach to managing acute non-specific low back pain with analgesic medicines” until higher quality trials comparing analgesics to each other are published.
Paracetamol, ibuprofen, and codeine are common analgesics used to treat acute non-specific low back pain that lasts less than six weeks. However, evidence for their comparative effectiveness is scant.
Researchers searched scientific databases for randomized controlled trials comparing analgesic medicines with another analgesic, placebo, or no treatment in patients with acute non-specific low back pain.
They included 98 randomized controlled trials published between 1964 and 2021 in their analysis, out of an initial 124 relevant trials. There were 15,134 participants aged 18 and up, and 69 different medicines or combinations were used.
Nonsteroidal anti-inflammatory drugs, paracetamol, opioids, anti-convulsant drugs, muscle relaxants, and corticosteroids were all tested in the trials. The researchers used a validated risk tool to assess their bias risk.
The main outcomes of interest were the intensity of low back pain at the end of treatment (on a 0-100 point scale) and safety (number of participants who reported any adverse event during treatment). At the start of each trial, the average pain intensity among participants was 65 out of 100.
The researchers found low or very low confidence in evidence for reduced pain intensity (around 25 points) after treatment with the muscle relaxant tolperisone, the anti-inflammatory drug aceclofenac plus the muscle relaxant tizanidine, and the anti-convulsant drug pregabalin versus placebo.
Evidence for large reductions in pain intensity (around 20 points) for four medicines, including the muscle relaxant thiocolchicoside and anti-inflammatory drug ketoprofen, moderate reductions (10-20 points) for seven medicines, including anti-inflammatory drugs aceclofenac, etoricoxib, and ketorolac, and small reductions (5-10 points) for three medicines, including ibuprofen and paracetamol, was also found to be lacking.
Evidence of low or very low confidence suggested no difference in the effects of several of these medications.
When tramadol, paracetamol plus sustained release tramadol, baclofen, and paracetamol plus tramadol were compared to placebo, the researchers found moderate to very low confidence evidence for increased adverse events such as nausea, vomiting, drowsiness, dizziness, and headache. Evidence of moderate to low confidence suggested that these medications may increase the risk of adverse events when compared to other medications.
The study also discovered moderate to low confidence evidence for other secondary outcomes, such as serious adverse events and treatment discontinuation, as well as a secondary analysis of medication classes.
Although this was a thorough review based on a thorough literature search, the researchers acknowledge that the majority of included studies had concerns about bias, which, along with other limitations, may have influenced the findings.
“Our review of analgesic medicines for acute non-specific low back pain discovered significant uncertainty regarding effects on pain intensity and safety,” they write. As a result, they advise clinicians and patients to “be cautious when using analgesic medications.”
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