The use of oral fluoroquinolones (FQs) poses the same level of fibromyalgia risk as other antibiotics such as amoxicillin and azithromycin, a study suggests.

The study, “Oral Fluoroquinolones and Risk of Fibromyalgia,” was published in the British Journal of Clinical Pharmacology.

Oral FQs, which are the most prescribed antibiotic, received a black box warning in 2016 from the U.S. Food and Drug Administration. The warning was based on severe side effects reported after the use of FQs that resembled fibromyalgia — widespread amplified pain in the muscles and joints. But the prevalence of this risk has not been quantified in detail.

Of significance, respiratory infections, for which FQs might be prescribed, may also lead to fibromyalgia, which could confuse the association between fibromyalgia and FQs.

In this study, researchers in Canada aimed to correlate the use of FQs to cases of fibromyalgia that were part of health claims filed between 2006 and 2016.

Using a large health claims database in the U.S., PharMetrics Plus, the team identified cases reported as fibromyalgia by a rheumatologist. All FQ prescriptions were identified, and only those individuals whose FQ prescription preceded their fibromyalgia diagnosis entry by three months to a year were included. Patients who were prescribed amoxicillin and azithromycin were also included.

Amoxicillin and azithromycin, which are chemically different from FQs, served as a control for any effects seen because of a bacterial or viral infection mimicking fibromyalgia.

The team identified 5,148 such cases and included 51,480 cases without a fibromyalgia diagnosis as controls. Of the 5,148 fibromyalgia cases with past FQ, amoxicillin, or azithromycin use, 87% were women.

Of these three antibiotics, the researchers found that the chances of a fibromyalgia diagnosis being associated with FQs was 1.63 times higher, amoxicillin 1.64 times higher, and azithromycin 1.68 times higher than in the control group. No significant difference was noted between the three antibiotic groups.

These results indicate that the risk of fibromyalgia with FQs is similar to that of amoxicillin and azithromycin, according to the authors.

“Despite the case reports of fibromyalgia and FQ use in both the literature and various drug regulatory agencies, risk seems to be similar with amoxicillin and azithromycin,” they wrote. “Risk might therefore be due to possible infection that triggered fibromyalgia symptoms.”