A trial has dashed hopes that antibiotics may benefit a subgroup of patients with chronic low back pain and Modic changes due to presumed bacterial discitis.
In 2013 Danish researchers found that 100 days of amoxicillin–clavulanate treatment relieved chronic back pain symptoms in patients with disc herniation.
They hypothesised that the antibiotic was effective because it treated low-grade infection by species such as P. acnes that is one of the hypothetical causes of the bone oedema underlying Modic type 1 changes.
But a second trial by a different group of Scandinavian clinicians has failed to confirm the effects of antibiotics in a group of 180 patients with chronic low back pain, previous disc herniation, and type 1 (n=118) or type 2 (n=62) Modic changes. In the new AIM study, patients were randomised to either three months of oral treatment with 750 mg amoxicillin or placebo three times daily.
But when followed up for one year, there was no clinically important benefit seen in the primary outcome of Roland-Morris Disability Questionnaire (RMDQ) score between antibiotic and placebo groups. A clinically important difference in RMDQ score was defined as at least 4, but the difference observed between the amoxicillin group and the placebo group was −1.6 (95% confidence interval −3.1 to 0.0, P=0.04).
The difference in mean RMDQ scores was −2.3 for patients with type 1 Modic changes and −0.1 for patients with type 2 Modic changes.
Analyses of secondary outcomes also found only clinically unimportant differences for measures such as pain related disability (Oswestry Disability Index 2.0), low back pain intensity (0-10 numerical rating scale), and health related quality of life.
Drug-related adverse events were seen in 56% of patients in the amoxicillin group compared with 34% in the placebo group.
The researchers said it was not clear why their trial had failed to replicate the promising findings of the earlier RCT, but noted they had set a high benchmark level of clinically relevant benefit equivalent, to that expected with NSAID treatment.
“It is our opinion that the numbers do not justify three months of treatment with antibiotics when we consider the increase in adverse events and the context of increasing antibiotic resistance worldwide,” they wrote.
“Therefore, our results do not support the use of antibiotic treatment for chronic low back pain and Modic changes,” they concluded.
In an online response, the lead author of the original trial strongly disputed the new findings, saying the new study did not replicate his own because it involved patients with lower levels of back pain disability and with both type 1 and 2 Modic changes.
Dr Hanne Albert pointed out that the new trial showed improvements in the patients with type 1 Modic changes and also noted major improvements in placebo group in the AIM study.
“Instead of adding to our body of knowledge in this field of back science the publication only serves to muddy the waters. This paper should be temporarily withdrawn until it has been rewritten and resubmitted so that the conclusions truly reflect the data,” he wrote.