Acetaminophen ineffective for chronic low back pain - now what?

- Jennifer Middleton, MD, MPH

Acetaminophen has been a mainstay of treatment for chronic low back pain (LBP) for years, but a recent study turns that conventional wisdom on its head.

In a meta-analysis that was published in the BMJ last month, Machado et al searched multiple medical literature databases looking for randomized controlled trials (RCTs) evaluating acetaminophen against placebo in patients with chronic "non-specific" low back pain, hip osteoarthritis (OA), or knee OA. They ended up with 13 RCTs of fair to high quality: 10 RCTs for hip and/or knee OA, and 3 RCTs for chronic LBP. All of the studies for chronic LBP were from 2014.

For chronic LBP, the authors found a non-significant difference for both pain and measures of disability for acetaminophen compared to placebo. For hip and/or knee OA, the difference was statistically significant but likely not clinically significant (only a 4 point difference on a 100-point scale).

Intuitively, acetaminophen seems like a reasonable choice for treating chronic LBP. It's inexpensive and relatively safe when used at recommended doses. A 2009 AFP article on treating chronic LBP advises a trial of acetaminophen prior to trying other medications; that recommendation was based on the best evidence available at the time. This 2015 meta-analysis, that includes newer studies, overturns that recommendation and should prompt a change in the clinical guidelines.

This study raises significant questions about appropriate treatments for this common condition. Opiates can cause dependence and addiction, and long-term NSAID use is also of questionable safety as discussed here in 2013. A 2011 AFP article describes non-pharmaceutical treatments for chronic LBP with some evidence of efficacy; back exercises, acupuncture, massage, spinal manipulation, behavioral therapy, and intensive multidisciplinary treatments programs are all reasonable treatments to offer patients. Perhaps chronic LBP treatment should focus more on these physical modalities and less on medications, though for some patients physical therapies alone may not be enough. Hopefully, we will see future studies addressing the care of patients with this common condition, because right now our medication treatment options feel limited with acetaminophen and NSAIDs both potentially off the table.

Keeping up with changes in the primary care evidence base can feel like a daunting task, even more so, perhaps, when new studies challenge assumptions that once seemed immutable. Chances are, your favorite journals have Twitter and Facebook accounts (AFP does!), and the print version of AFP also includes a round-up of recent evidence-base game changers in its "Cochrane for Clinicans" and "AFP Journal Club" sections.

How do you care for patients with chronic LBP? Will this meta-analysis change your practice?