Safety, Efficacy of Analgesics for Low Back Pain 'Uncertain'

Pauline Anderson

March 27, 2023

Despite decades of research, there's still considerable uncertainty about the comparative effectiveness and safety of analgesics for the treatment of acute low back pain, new research shows.

Higher-quality randomized controlled trials of head-to-head comparisons are needed, study investigator Michael A. Wewege, PhD candidate, research fellow, University of New South Wales and Neuroscience Research Australia, Sydney, told Medscape Medical News.

"Until then, doctors should use caution when prescribing analgesic medicines for adults with nonspecific acute low back pain. They should use this new evidence in line with their own expertise and the patient sitting in front of them when making any decision about a medication," he added.

The findings were published online March 22 in the BMJ

Poor Quality Evidence

Analgesics such as ibuprofen, acetaminophen, and codeine are widely used to treat nonspecific low-back pain, which is defined as pain lasting less than 6 weeks. However, evidence for the comparative efficacy of these agents is limited.

To fill this knowledge gap, the researchers conducted a systematic review and analysis of controlled trials comparing analgesics with another analgesic, placebo, or no treatment in patients with acute, nonspecific low back pain.

The review involved 98 randomized controlled trials that included 15,134 adults (49% women) aged 30-60 years with pain duration ranging from 24 hours to 21 days. The median baseline pain intensity was 65 on a pain scale of 0 to 100.

Of the included trials, 39% were placebo controlled, 67% masked both participants and clinicians, and 41% reported industry sponsorship.

The studies compared an analgesic medicine with another analgesic, placebo, or no treatment comprised of usual care or being placed on a wait list.

Study medications, which had to be approved in the United States, UK, Europe or Australia, included nonsteroidal anti-inflammatory drugs, paracetamol, opioids, anticonvulsants, antidepressants, muscle relaxants, and corticosteroids.

These drugs were administered systemically as a single drug or in combination formulations, at any dose.

Researchers used a network meta-analysis, which combines direct and indirect information across a network of randomized clinical trials to estimate the comparative effectiveness of multiple treatments.

The primary outcomes were reductions in low back pain intensity (measured with a visual analogue scale), numerical rating scale or another ordinal scale, and safety as indicated by the number of participants who had any adverse event.

Investigators found several medications were associated with large reductions in pain intensity compared with placebo, but with low or very low confidence.

Low or very low confidence was found for reduced pain intensity after treatment with tolperisone (mean difference −26.1; 95% CI, −34.0 to −18.2), aceclofenac plus tizanidine (mean difference −26.1; 95% CI, −38.5 to −13.6), pregabalin (mean difference, −24.7; 95% CI, −34.6 to −14.7), and 14 other medicines compared with placebo, the researchers report.

In addition, they found low or very low confidence for no difference between the effects of several of these medications.

Increased adverse events had moderate to very low confidence with tramadol (risk ratio 2.6; 95% CI, 1.5 - 4.5), paracetamol plus sustained release tramadol (RR, 2.4; 95% CI, 1.5 - 3.8), baclofen (RR, 2.3; 95% CI, 1.5 - 3.4), and paracetamol plus tramadol (RR, 2.1; 95% CI, 1.3 - 3.4) compared with placebo, the investigators add.

"These medicines could increase the risk of adverse events compared with other medicines with moderate to low confidence. Moderate to low confidence was also noted for secondary outcomes and secondary analysis of medicine classes," the researchers note.

The review suggested 14 additional comparisons favored the treatment over placebo, all with very low confidence except for one with low confidence.

In the 68 trials that included the number of participants reporting an adverse event, there was moderate confidence for increased adverse events with the opioid tramadol (RR, 2.6; 95% CI, 1.5 - 4.5), paracetamol plus sustained release tramadol (RR, 2.4; 95% CI, 1.5 - 3.8), and paracetamol plus tramadol (RR, 2.1; 95% CI, 1.3 - 3.4), and low confidence for baclofen (RR, 2.3; 1.5 - 3.4), compared with placebo.

The review also uncovered moderate to low confidence for secondary outcomes, which included low back-specific function, serious adverse events, and acceptability (number of participants who dropped out).

Unexpected Findings

The new results were somewhat unexpected, said Wewege.

"When we set out to do this review, we envisioned the evidence would be a lot more comprehensive. We didn't think it would be so disconnected and there would be so few trials looking at the different comparisons that would lead us to have low confidence in most of the findings."

Various factors contributed to this low confidence, he said. One was the risk of bias — about 90% of trials had some concerns or high risk of bias. Another factor was the heterogeneity in effect estimates.

Most of the evidence is based on studies comparing different analgesics to placebo, Wewege noted. The lack of head-to-head drug comparisons is because "the easiest way to get a drug approved is just to demonstrate it's better than placebo," he said.

In addition to these new findings, clinicians should consider a medication's availability, their own expertise, and patient preferences when selecting an analgesic, said Wewege. He noted most patients with acute low back pain get better within a few weeks without any intervention.

"Patients should be reassured that things will heal naturally and that they are not going to be in pain forever," he said.

Determining Optimal Treatment Is Key

Commenting for Medscape Medical News, Chris Gilligan, MD, associate chief medical officer, Brigham and Women's Hospital, and associate professor of anaesthesia, Harvard Medical School, Boston, Massachusetts, said determining which medications are optimal is "key," as acute low back pain is very common and analgesics are used frequently.

The new review does provide information on which medications have the strongest evidence for pain reduction, said Gilligan. "On the one hand, it directionally points you towards certain medications, and even certain classes of medication, for comparative effectiveness."

However, he said, the confidence for this effectiveness is low or very low, "so I wouldn't overweight it."

The data on adverse effects, where the confidence is mostly moderate to low, might have more of an influence on prescribing, he said.

"For example, there's some indication tramadol may be more closely associated with adverse events in patients with acute low back pain and that would add to our caution about using tramadol; it's not that we would never use it, but would take that into account."

Gilligan agrees clinicians should be cautious about prescribing analgesics for low back pain. One reason for being conservative in terms of treatments, he noted, is that "acute low back pain has a very favorable natural history."

While clinical practice guidelines recommend nonpharmacologic therapies as first- and second-line treatment for acute, nonspecific low back pain, Gilligan noted that as with drugs, evidence for nondrug therapies also has low or very low confidence.

The study received funding from a 2020 Exercise Physiology Research (Consumables) Grant from the University of New South Wales, which was used to obtain translations of studies published in languages other than English.

Wewege was supported by a Postgraduate Scholarship from the National Health and Medical Research Council of Australia, a School of Medical Sciences Top-Up Scholarship from the University of New South Wales, and a PhD Supplementary Scholarship from Neuroscience Research Australia. Gilligan reports that he conducts clinical trials with companies and groups, including the National Institutes of Health (NIH) related to medications, devices, and procedures for pain.

BMJ. Published online March 22, 2023. Full text

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