Evaluation of the clinical utility of measuring serum infliximab and vedolizumab concentrations during monitoring of biologic therapy in patients with inflammatory bowel disease

Introduction
Infliximab (IFX) and vedolizumab (VDZ) are monoclonal antibodies used for the treatment of inflammatory bowel diseases (IBD), such as Crohn’s disease (CD) and ulcerative colitis (UC). The concentration of biologic drugs must be high enough for a therapeutic response.

Aim
To evaluate the association of VDZ or IFX concentrations with the clinical condition of patients with IBD during therapy.

Material and methods
We examined 82 patients with IBD treated with VDZ or IFX. Blood samples were before the administration of the drug dose. Serum drugs were determined by ELISA with RIDASCREEN kits from R-Biopharm AG.

Results
The highest median serum VDZ concentrations were observed in patients with UC and endoscopic response or remission. The median serum VDZ concentration during the maintenance phase in patients with endoscopic remission remained at similar levels, while in patients without remission, a decrease was shown. Additionally, analysis of VDZ concentrations in the group of patients without endoscopic remission showed a significant decrease in drug concentration in the maintenance phase compared the induction phase (p = 0.037). VDZ concentration of 26.4 µg/ml differentiated patients with endoscopic remission from patients who did not respond. In the group of CD patients, up to 91% of the patients responded to IFX treatment in the maintenance phase.

Conclusions
The sustained serum concentrations of VDZ in patients with IBD determined in the maintenance phase confirmed a positive response to this therapy, which in practice may have significance in optimising the dosage of biological treatment.