Serum levels of infliximab in Brazilian patients with Crohn's disease: what are the reasons for differences from previous studies?

Authors' Reply – Comments: Serum levels of infliximab in Brazilian patients with Crohn's disease: what are the reasons for differences from previous studies?

“…We would like to thank Teixeira et al 1 for their comments on our article 2. They correctly noted that the majority of our patients presented infliximab (IFX) levels above the therapeutic concentration, differing from three other Brazilian studies published between 2017 and 2018 3-5.…”

“…Concerning the comments of Teixeira et al 1 about why we might have mixed the results of the study because several patients with levels between 3-6 µg/mL would be considered adequate according to the range of 3-7 µg/mL but infratherapeutic according to our adopted range (6-10 µg/mL), we would like to clarify that, as described in our manuscript 2, there were no patients with levels between 3-6 µg/mL. Of the few patients we had with IFX trough levels ≤ 5 µg/mL, all presented undetectable levels (<0.035 µg/mL), and they correlated 100% with positive ATIs, demonstrating the accuracy of the test.…”

“…Regarding the therapeutic window noted by Teixeira et al 1, Ungar et al 12 found a significant association between anti-TNF-α serum levels and mucosal healing, which led to the recommendation that a serum level of 6-10 μg/mL for IFX is necessary to achieve healing of 80%-90% of IBD patients, which may be considered a therapeutic window as well. Moreover, this interval was followed in other studies in the literature 13-15.…”