Abstract
Background: Primary lack or secondary loss of response to therapy with infliximab is a significant problem. This study aimed to evaluate the response to treatment in patients with Crohn’s disease (CD) and ulcerative colitis (UC) achieving therapeutic and sub-therapeutic trough levels of biosimilar infliximab (CT-P13). Results: A total of 65 patients (32 with CD and 33 with UC) were recruited. The overall response rate in both CD and UC patients exceeded 80%. There were no significant differences in treatment response and CT-P13 levels for patients with CD or UC. We did not find significant differences in the percentage of patients achieving drug levels of 3 μg/mL at week 6, 10, or 12; a significant decrease was observed at week 14. Up to 55.5% of patients with CD and 64.3% of patients with UC with sub-therapeutic CT-P13 levels at week 14 primarily responded to treatment. Conclusions: Intermediate measurements of drug levels at weeks 10 and 12 did not capture any pronounced decrease in infliximab concentrations below therapeutic levels in either group, thus suggesting no clinical usefulness. A significant percentage of patients primarily responded to treatment despite sub-therapeutic drug levels after the induction phase.