P440 Therapeutic drug monitoring of infliximab for the management of loss of response in inflammatory bowel disease: an observational multicenter study

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Background: Therapeutic drug monitoring (TDM) of infliximab for inflammatory bowel disease (IBD) is being increasingly proposed, particularly for managing the loss of response (LOR), as an alternative to empirical dose adjustment. Our aim was to verify in a prospective multicenter cohort the usefulness and cost-effectiveness of applying an algorithm based on TDM, modified from Steenholdt C. et al. 2014.

Methods: We recruited consecutive IBD patients, experiencing a LOR to infliximab while on maintenance therapy from at least 4 months, for which the assay of infliximab trough levels (ITL) and of antibodies to infliximab (ATI) was available for subsequent therapeutic decisions. We compared this cohort with a retrospective one composed of patients for which a serum sample was collected at the time of LOR diagnosis although the clinical decisions were made blinded to ITL and ATI results. We evaluated the clinical outcome after 12 weeks, also in term of direct costs for anti-TNF therapy, verifying the agreement with an algorithm considering a therapeutic ITL cut-off of 3 ug/ml. ITL and ATI were assayed by ELISA technique (Lisa Tracker-Duo® Infliximab, Theradiag, Marne-la-Vallée, France).

Results: Ninety-six patients were evaluable in the prospective cohort, and they were compared with 52 retrospectively studied. The two cohorts were similar in characteristics and distribution of TDM results. In the prospective cohort, however, we observed that less optimizations (infliximab dose increase and/or interval decrease) were performed compared to the retrospective one (45% versus 71%, p=0.003). In parallel, more patients were shifted to adalimumab in the prospective cohort than in the retrospective one (25% versus 4%, p=0.001). No difference was detected among the two cohorts in terms of clinical efficacy of the therapeutic modifications: the percentage of patients achieving a clinical response at 12 weeks were 52% and 54%, respectively. However, we estimated a cost saving of up to 98.872 Euros if the algorithm was correctly applied to the retrospective cohort, avoiding unjustified dose optimizations in 28 cases, with a global cost for TDM of 4.160 Euros for the whole retrospective cohort.

Conclusions: In our IBD population, applying TDM for infliximab LOR management resulted in 26% less drug dose optimizations, without loss of efficacy as compared to empirical treatment adjustment. TDM use in LOR management appears to be cost-effective, allowing a more rational use of infliximab without unjustified dose intensification.

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