Antibiotic treatment confers no benefit to patients with chronic low back pain, Modic changes

Oral antibiotic treatment for 3 months does not provide a clinically important benefit to patients with chronic low back pain, previous disc herniation and vertebral endplate (Modic) changes as compared with placebo, according to a Norway study.

“[W]e were not able to replicate the findings of the previous randomized trial,” the researchers said. “Our results do not support the use of antibiotic treatment for chronic low back pain and Modic changes.”

A total of 180 patients with chronic low back pain, previous disc herniation, and type 1 (n=118) or type 2 (n=62) Modic changes enrolled from June 2015 to September 2017 were included in this double-blind, parallel group, placebo-controlled, multicentre trial. Patients were randomly assigned to 3 months of oral antibiotic treatment with either 750-mg amoxicillin or placebo three times daily. A computer-generated number on the prescription was used to conceal the allocation sequence.

The primary outcome was the Roland-Morris Disability Questionnaire (RMDQ) score (range, 0–24) at 1-year follow-up in the intention-to-treat population. The predefined, minimal clinically important between-group difference in mean RMDQ score was 4.

At 1 year, between-group difference in the mean RMDQ score was –1.6 (95 percent confidence interval [CI], –3.1 to 0.0; p=0.04) in the primary analysis of the total cohort. The secondary analysis revealed a between-group difference of –2.3 (95 percent CI, –4.2 to –0.4; p=0.02) in the mean RMDQ score for patients with type 1 Modic changes and –0.1 (95 percent CI, –2.7 to 2.6; p=0.94) for those with type 2 Modic changes. [BMJ 2019;367:l5654]

More patients in the amoxicillin group experienced at least one drug-related adverse event than in the placebo group (50 [56 percent] vs 31 [34 percent]).

“Our results are not consistent with the findings of the trial we were reassessing, which showed a substantial effect (between-group difference, 8.3) in patients who received a combination treatment of amoxicillin and clavulanic acid for 3 months,” the researchers said. [Eur Spine J 2013;22:697-707]

The current study used amoxicillin without clavulanic acid. However, the researchers did not consider this difference in treatment regimens as the explanation for the inconsistent trial results, noting little or no resistance to penicillin among C acnes in vitro and that penetration of discs by clavulanic acid was poor. [Anaerobe 2006;12:207-210; J Bone Joint Surg Br 1995;77:967-970; Eur Spine J 1993;2:145-148]

Compared with the former trial, the current one included a lower percentage of patients with previous disc surgery (52 percent vs 20 percent) and had relatively more patients at follow-up in the antibiotic group (96 percent vs 86 percent). This might have impacted the differences in results, according to the researchers.

“The improvement in RMDQ score from baseline to 1 year follow-up in the placebo group was smaller in the previous trial (from 15.0 to 14.0 vs 12.8 to 10.7 in our trial),” they said. “It is difficult to evaluate whether this could have been owing to poor blinding in the previous study because data on blinding efficacy were lacking.”