Fluoroquinolones and the aorta

Do fluoroquinolone antibiotics cause aortic pathology? In a linked article (doi:10.1136/bmj.k499), Pasternak and colleagues report a population based study of the association between outpatient treatment with fluoroquinolones (principally ciprofloxacin and norfloxacin) and aortic aneurysms and dissection.1 Compared with patients prescribed amoxicillin, those prescribed fluoroquinolones had a 66% increase in the 60 day risk of aortic aneurysm or dissection (hazard ratio 1.66, 95% confidence interval 1.12 to 2.46).

This is not the first study to explore this question, but from a methodological perspective it is arguably the strongest. Unlike in earlier studies,23 Pasternak and colleagues used an active comparator (amoxicillin). This makes obvious sense, because patients treated with antibiotics are systematically different from those who are not. Other strengths included a large sample size, comprehensive prescription data, and well balanced characteristics between groups at baseline, owing to propensity score based matching.

But do fluoroquinolones actually cause aortic pathology? It is sometimes said that observational studies cannot prove a …