1. A three-month course of amoxicillin provides no clinically significant benefit over placebo for treatment of chronic back pain with previous disc herniation and type 1 or 2 Modic changes.
Evidence Rating Level: 1 (Excellent)
As current management strategies for chronic low back pain offer low to moderate improvement in pain and disability, efforts to identify subgroups of patients who may benefit from specific treatments are underway. There is some evidence to suggest that chronic back pain with endplate changes in vertebral bone marrow (Modic changes) may reflect low-grade bacterial discitis by Cutibacterium acnes via bloodstream source, and that antibiotic treatment may be effective in reducing pain and disability in this subgroup. The AIM study examined the efficacy and harm of three months of oral amoxicillin therapy for patients with chronic low back pain and type 1 or 2 Modic changes. Using a multi-centre, double-blind, parallel group design with a three-month treatment phase and a nine-month follow-up phase, adults with chronic low back pain of at least moderate intensity, lumbar disc herniation on recent magnetic resonance imaging, and type 1 or type 2 Modic changes were recruited from outpatient clinics from six Norwegian hospitals between 2015 and 2017. Participants (n=180) were randomized to three months of oral amoxicillin 750 mg three times daily or placebo (maize starch). The primary outcome of interest was the validated Norwegian Roland-Morris Disability Questionnaire (RMDQ) score at one-year follow-up in an intention-to-treat population. The minimal clinically important between-group difference was pre-defined at 4 for this measure. Researchers found a non-clinically important difference in the amoxicillin treatment group at one-year follow-up in terms of mean RMDQ scores (mean difference -1.6, 95% CI -3.1 to 0.0, p=0.04). Adverse events occurred in 56% of patients in the treatment group, compared to 34% in the placebo group. The findings of this study therefore suggest that three-month amoxicillin therapy in chronic low back pain patients with previous disc herniation and Modic changes do not provide a clinically-important benefit compared to placebo.