Clinical Use of Infliximab Trough Levels and Antibodies to Infliximab in Pediatric Patients With Inflammatory Bowel Disease.

Objectives: Optimizing infliximab (IFX) treatment in pediatric patients with inflammatory bowel disease (IBD) by using serum infliximab (S-IFX) trough levels and antibodies to IFX is recommended. There is need for studies assessing this strategy in clinical practice.

Methods: We retrospectively identified all pediatric patients with IBD (n = 146, median age 14.8 years) treated with IFX at our tertiary referral center from 2003 to 2014. All were analyzed for IFX trough levels (S-IFX, n = 475), and IFX antibody (IFX-Ab, n = 219) titers were included. Both were analyzed using enzyme-linked immunosorbent assay. We correlated these parameters with concurrently analyzed fecal calprotectin levels and the treatment outcome.

Results: If IFX had no efficacy, or a loss of response occurred, 40 of 64 (63%) had trough levels <2.0 mg/L, with negative IFX-Ab in 37 of 59 (63%). If the S-IFX was very low (<0.2 mg/L), 4 of 36 still had negative IFX-Ab. Concurrent azathioprine therapy did not relate to IFX-Ab. Fecal calprotectin was significantly lower in patients with clinical remission or ongoing therapy compared with those with subsequent loss of efficacy: medians 95 μg/g (33-308) and 670 μg/g (264-1473), P < 0.0001. The S-IFX median was substantially higher in patients with either remission or ongoing therapy, compared with those with no or loss of efficacy: 3.7 mg/L (1.8-5.4) and 1.2 mg/L (0.03-4.4, P = 0.01), respectively.

Conclusions: Measuring IFX trough levels and fecal calprotectin has a potential impact on the treatment strategies and should be included in clinical routine. Low IFX trough levels associate with increased antibodies to IFX in most, but not in all cases.