Measuring of serum infliximab (IFX) induction concentrations might reduce primary non-response rates in inflammatory bowel diseases (IBD), but optimal target concentrations are unclear. We investigated whether IFX induction concentrations predict short-term endoscopic response at week 12 or treatment persistence at week 52.Sixty-nine IBD patients (Crohn's disease, n=24; ulcerative colitis, n=45) received standard IFX induction of 5 mg/kg bodyweight at weeks 0, 2, and 6. Responders continued maintenance therapy and underwent follow-up until week 52 or treatment discontinuation. We measured IFX concentrations at weeks 2, 6, and 12, and evaluated treatment response around week 12 with endoscopy or with clinical scores and fecal calprotectin. Using the receiver operating characteristic analysis, we determined optimal IFX concentration thresholds associated with treatment response. We further compared IFX induction concentrations between patients persisting on IFX at week 52 and patients discontinuing treatment due to insufficient response.Responders (74%, 51 out of 69 patients) had significantly higher median IFX concentrations than non-responders at weeks 6 (25.06 vs. 19.68 µg/ml; P = 0.04) and 12 (18.03 vs. 10.02 µg/ml; P = 0.03), but not at week 2 (33.12 vs. 34.20 µg/ml; P = 0.97). Optimal IFX concentration thresholds for induction response were 21.33 and 5.13 µg/ml at weeks 6 and 12, respectively. Fifty-three patients continued IFX maintenance therapy until week 52. Induction concentrations failed to predict persistence on IFX therapy at week 52.Higher IFX induction concentrations predict endoscopic short-term response. However, induction concentrations failed to predict long-term persistence on IFX treatment.
