However, results from a cross-sectional study, in which several markers of oxidative stress were measured and average duration of treatment with azithromycin was 38 ± 22 months, are not consistent with this explanation of our findings as levels of serum 15-F2t-isoprostane, total antioxidant capacity, superoxide dismutase activity, catalase activity, glutathione peroxidase activity, and thiobarbituric acid reactive substances, in CF patients who had been taking azithromycin (n = 23) and in CF patients who had not been receiving azithromycin (n = 13) were similar (Olveira et al., 2017). Here, CAT is linked to cystic fibrosis.