Guidelines are just the start
While some guidelines support serotonin norepinephrine reuptake inhibitors (SNRIs) as treatments for back pain, a new systematic review and meta-analysis of existing research found no firm evidence of a benefit. Adverse effects, however, are common.
“Our review shows that, although these medicines are effective, the effect is small and unlikely to be considered clinically important by most patients,” wrote the authors of the review, which appeared Jan. 20 in the BMJ. “Our review also showed that about two-thirds of patients using SNRIs experience adverse events.”
However, the report hinted that certain classes of antidepressants may provide significant relief in knee OA and sciatica.
According to a 2018 review, 10 of 15 clinical guidelines from around the world – including those of the American College of Physicians – recommended antidepressants as treatments for low back pain, and 2 advised against them. “Evidence supporting the use of antidepressants is, however, uncertain,” wrote the authors of the new review, led by Giovanni E. Ferreira, PhD, of the University of Sydney. “Systematic reviews of antidepressants for back pain and osteoarthritis have either not included several published trials, considered only one type of antidepressant (e.g., duloxetine), or failed to assess the certainty of evidence.”
For the new review, the authors analyzed 33 randomized, controlled trials with a total of 5,318 subjects. Both published data and unpublished data from clinical trial registries were included.
Back pain trials
A total of 19 trials examined back pain, mostly lower back pain (16 trials), and none lasted more than 1 year. Fifteen examined SNRIs while others looked at other kinds of antidepressants.
The researchers found that “the effect of SNRIs was small [on back pain] and below this review’s predetermined threshold of clinical importance. ... Evidence ranging from low to very low certainty showed no benefit of a range of antidepressant classes, including SSRIs [selective serotonin reuptake inhibitors], tetracyclic antidepressants, SARIs [serotonin antagonist and reuptake inhibitors], and NDRIs [norepinephrine and dopamine reuptake inhibitors] for pain and disability across follow-ups of 2 weeks or less, 3-13 weeks, and 3-12 months.”
Sciatica trials
Six trials examined antidepressants as treatments for sciatica. Very-low-certainty evidence suggested that SNRIs reduced pain at up to 2 weeks (1 trial, n = 50) but not at 3-13 weeks (3 trials, n = 96). The results of trials of tricyclic antidepressants (TCAs) were the opposite: low- to very-low-certainty evidence suggested the drugs didn’t reduce pain at up to 2 weeks (2 trials, n = 94) but did at 3-13 weeks (2 trials, n = 114) and 3-12 months (1 trial, n = 60).
“All sciatica trials were small, had imprecise estimates, and were at high risk of bias, which reduced the certainty of evidence to low and very low,” the authors cautioned. “This level of uncertainty indicates that the true estimate of effect of TCAs and SNRIs for sciatica is likely to be substantially different from what we estimated in our review.”
Knee OA trials
Eight trials examined SNRIs in knee OA. Moderate-certainty evidence linked the drugs to less pain at up to 2 weeks (four trials, n = 1,328) and low-certainty evidence linked them to less pain at 3-13 weeks (eight trials, n = 1,941). Low-certainty evidence also linked the drugs to less disability at 2 weeks or less (one trial, n = 353) and 3-13 weeks (seven trials, n = 1,810).
In knee OA, “the effect of SNRIs was small and below this review’s predetermined threshold of clinical importance,” the researchers wrote. “However, the lower limit of the confidence interval did contain clinically important effects for pain, but not for disability.”
Antidepressant side effects in trials
A total of 21 trials (n = 4,107) looked at side effects when antidepressants were studied as treatments for back pain and OA. Low-certainty evidence in 13 SNRI trials (n = 3,447) suggested a higher risk of any adverse events in antidepressant versus placebo (62.5% vs. 49.7%; relative risk, 1.23, 95% confidence interval, 1.16-1.30), but there was no significantly higher risk of serious adverse events in 10 SNRI trials with 3,309 subjects (1.6% vs. 1.3%; RR, 1.12, 95% CI, 0.61-2.07).
As for adverse effects of non-SNRIs, “the number of studies evaluating the safety of other antidepressant classes was small, trials were underpowered to detect harm, and the certainty of evidence ranged from low to very low,” the researchers wrote.
Going forward, the authors said that “large, definitive randomized trials that are free of industry ties are urgently needed to resolve uncertainties about the efficacy of antidepressants for sciatica and osteoarthritis highlighted by this review.”
‘Largely ineffective’ drug treatments
In an accompanying commentary, Martin Underwood, of the University of Warwick in Coventry, England, and Colin Tysall, of the University Hospitals of Coventry and Warwickshire, also in Coventry, noted that “drug treatments are largely ineffective for back pain and osteoarthritis and have the potential for serious harm. We need to work harder to help people with these disorders to live better with their pain without recourse to the prescription pad.”
However, they noted that SNRIs may still be helpful for patients with back pain or OA. “Absolute effect sizes for physical treatments for low-back pain are of similar magnitudes to those reported here and translate into numbers needed to treat of between five and nine. If the same were true for SNRIs, some people might choose to a try that option for a 1 in 10 chance of a worthwhile reduction in pain after 3 months. They can easily stop if treatment is ineffective or does not suit them.”
The research received no specific funding. The review authors disclosed relationships with GlaxoSmithKline (postgraduate scholarship), Pfizer (investigational product for two trials), and Flexeze (provision of heat wraps for a trial). Mr. Underwood reported being a director and shareholder of Clinvivo. Mr. Tysall reported no disclosures.