Infliximab (IFX) has changed the treatment of inflammatory bowel disease (IBD). It has made it possible to achieve deep remission and thereby reduced the need for surgical interventions associated with advanced disease. However, with a significant proportion of patients either not responding to treatment or experiencing a decline in its efficacy, exploring new approaches to optimize treatment is reasonable. Studies suggest that some patients require higher IFX serum concentrations to achieve remission, therefore individualized dosing adjustments based on therapeutic drug monitoring (TDM) could lead to improved long-term clinical outcomes.
The aim of this study was to determine how IFX serum concentrations correlate with IBD treatment efficacy and safety and how they correlate with the biochemical inflammation marker C-reactive protein (CRP). We also investigated whether there is a threshold for IFX serum concentrations that could distinguish between patients with active disease and those in remission.
We conducted a retrospective study that included 164 patients with IBD, managed at the Department of Gastroenterology University Medical Centre Ljubljana, who received maintenance pharmacotherapy with IFX between January 2018 and October 2020. Its dosing was based on proactive TDM approach with individualized dosage adjustments according to the continuous determination of IFX serum concentrations. The results of the time-to-treatment discontinuation analysis were encouraging, as only 18/164 (11,0 %) patients required IFX discontinuation, 9 (5,5 %) due to loss of efficacy and 9 (5,5 %) due to safety complications (infections, skin side effects). IFX serum concentration had no statistically significant effect on the risk of patients discontinuing treatment with IFX due to loss of efficacy (Hazard Ratio (HR): 0,973; 95 % Confidence Interval (CI): 0,806 – 1,174; p = 0,775), infections (HR: 0,790; 95 % CI: 0,554 – 1,126; p = 0,192) or skin side effects (HR: 0,961; 95 % CI: 0,766 – 1,206; p = 0,731). We confirmed a negative correlation between IFX serum concentrations and CRP, but only at the final time point (ρ = – 0,354; p = 0,002). We found that patients with low IFX serum concentrations had higher median CRP levels (7 mg/L; Interquartile Range (IQR): 5 – 17 mg/L) than patients with intermediate (5 mg/L; IQR: 5 – 34 mg/L) and high (5 mg/L; IQR: 5 – 26 mg/L) IFX serum concentrations (p = 0,001). We also found that patients who maintained high IFX serum concentrations during maintenance treatment, were more likely to have normal CRP after 24 months of the study. These patients had significantly higher median IFX serum concentrations (8,7 µg/mL; IQR: 4,4 – 24,0 µg/mL) than patients with elevated CRP (2,8 µg/mL; IQR: 0,5 – 8,1 µg/mL) (p = 0,001). The optimal threshold for IFX serum concentrations at the start of the study was determined at 5,68 µg/mL with a sensitivity of 62,5 % and a specificity of 79,0 % (Area Under the ROC Curve: 0,720; 95 % CI: 0,492 – 0,947; p = 0,044). Patients whose IFX serum concentrations at the start of the study were greater than 5,68 µg/mL, were almost three times more likely to achieve remission after 2 years than patients who did not reach this threshold (positive likelihood ratio: 2,97).
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