Measuring infliximab and adalimumab blood levels in IBD patients, prospective observations from a single center compared to a time period before regular use of these measurements.

This investigator-initiated prospective observational cohort study will explore the differences between two cohorts:

Prospective cohort: A structured format for TDM-assisted, clinical decision making in regard to IFX and ADM for IBD was implemented as standard care in our hospital group. In this strategy, serum trough levels of both biologicals will be measured at pre-specified moments to structure the use of these expensive therapies: after remission induction, in case of a proven disease flare or when an alteration in treatment regimen of the biological or immunomodulatory drug is considered. An algorithm for interpretation of drug levels and advisory treatment alteration is given for each specific measurement occasion. These strategies were developed by reviewing available literature on the application of TDM under different circumstances. An overview of the newly implemented strategy can be requested from the corresponding author. The strategy combines TDM with three IBD-specific patient-reported outcome measures, translated and validated for Dutch IBD patients. These measures were added to systematically compare patients IBD related symptoms in relation to TDM and biomarkers.

Historical cohort: in a timeframe where infliximab and adalimumab had an established place in the treatment of IBD, but dose alterations and treatment optimizations were based on clinical signs and symptoms. TDM for the analysis of anti-drug antibodies was freely available, but not part of standard care. The care provided in this cohort is in accordance with the current national treatment guidelines for IBD.

Proactive and reactive trough level measurements of TNFalpha blockers are useful in standard care by aiding an individualized treatment strategy, preventing loss of efficacy and reducing disease flares, while being more cost-effective than symptom-based treatment alterations.

Data from both cohorts will cover one year, the historical cohort from 01-01-2016 up to 01-01-2017 and the prospective cohort from 01-09-2018 up to 01-09-2019. For both cohorts, patients initiating infliximab or adalimumab therapy during these periods, data collection will cover a year onwards from starting therapy. As patients cannot all be included on the actual day of commencing the prospective observational study, we will ask permission to collect any data from 01-09-2018 up to consent, retrospectively. Data on the historical cohort will be collected in the time period of the prospective cohort. We aim to start inclusion from 01-11-2018 onwards. Data analysis and manuscript formation will commence starting November 2019 and are estimated to take up to the November 2020.

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