Objective: Therapeutic drug monitoring (TDM) of infliximab (IFX) is not routinely implemented in our clinical practice. We therefore carried out a prospective cohort study measuring IFX trough levels in our total inflammatory bowel disease (IBD) population in relation to remission.
Methods: Patient demographics, and medication and clinical history were collected from the electronic hospital information system. Blood was drawn at one time point for the determination of IFX trough levels and antibodies to IFX (ATI). Disease activity indices [Crohn's disease activity index (CDAI) and the Truelove-Witts disease activity index (TWDAI) for Crohn's disease and ulcerative colitis, respectively] and quality-of-life scores (Visual Analog Scale) were obtained.
Results: We included 107 patients. IFX levels varied from less than 0.02 to 21.9 μg/ml. The median IFX level was 2.8 μg/ml [interquartile range (IQR) 1.37-5.13]. The IFX level was associated significantly with remission (P=0.007). The median IFX level was 3.9 μg/ml (IQR 1.9-6.53) in patients in remission and 2.1 μg/ml in patients with active disease (IQR 0.77-4.38) (P=0.074). Receiver operating charecteristic curve analysis indicated a cutoff value of 2.18 μg/ml for CD and 6.26 μg/ml for UC. Eleven patients (10.3%) had developed ATI. The appearance of ATI was associated with the disappearance of IFX [relative risk: 2.2 (95% confidence interval: 1.368-3.610) P<0.0001], but not with relapse. The presence of ATI induced more infusion reactions [relative risk: 11.7 (95% confidence interval: 2.74-49.60) P<0.001].
Conclusion: TDM of IFX in IBD outpatients in a teaching hospital setting showed large interindividual differences in IFX trough levels. Despite this, we still found a significant association between remission and IFX trough levels. We determined cutoff values for both IBD modalities. IFX trough levels were not detectable in a significant proportion of IBD patients; TDM is indicated to identify this group of patients.