P386 Association of Infliximab Trough Levels and Perianal Disease Activity in Crohn’s Disease

Infliximab (IFX) has been proven to be efficacious in the treatment of perianal disease in patients with Crohn's disease (CD). Previous studies have shown a correlation between higher IFX trough levels and perianal fistula healing. We aimed to replicate these findings using a larger cohort of patients with Crohn’s disease. Retrospective cohort study including consecutive patients with Crohn's disease and perianal disease receiving treatment with infliximab between January 2016 and October 2018. Drug levels were compared between patients with active and inactive perianal disease. Active perianal disease was defined as an active draining fistula at physical examination and/or magnetic resonance imaging. Patients with unavailable IFX trough levels and/or without clinical information were excluded. A total of 252 measurements from 48 patients were available. Median age was 39 (22–80) and 26 (54.2%) were male. Forty-two (87.5%) patients were under concomitant immunomodulators. The majority (n = 40) of patients had ileo-colonic disease (L1: 62.5%, L2: 18.8% , L3: 18.8%). Median IFX trough levels were significantly higher in patients with inactive perianal disease (n = 230) compared with patients with active disease (n = 22): [median 5.89 - 16.38 vs. 3.98 −9.28, p = 0.014]. Using the median off all IFX trough levels for each patient, the AUROC for perianal remission was 0.818 (95% CI: 0.649–0.987). An IFX >5.55 μg/ml presented high positive predictive value 97.0% (95% CI: 83.3–99.5), high specificity 88.89% (95% CI: 51.9–99.7) albeit with low sensitivity 68.09% (95% CI: 52.9–80.9) for perianal disease remission. There is a significant association between IFX trough levels and fistula healing in Crohn’s disease. Therapeutic drug monitoring aiming at higher IFX trough levels may be beneficial in this hard to treat population.