Vedolizumab Trough Levels in Children with Anti-TNF Refractory Inflammatory Bowel Disease.

OBJECTIVES Inflammatory bowel disease (IBD) can be successfully treated with vedolizumab. Studies in adult IBD patients have shown that differences in response to vedolizumab may be related to variability in vedolizumab trough levels, but in children with pediatric-onset IBD data regarding vedolizumab trough levels are not available. Thus far, the role of trough levels in pediatric-onset IBD treatment remains unclear. We aimed to investigate predictors of vedolizumab trough levels in pediatric-onset IBD patients. METHODS Data from anti-TNF refractory pediatric-onset IBD patients who received vedolizumab were collected retrospectively. Vedolizumab trough levels were measured in serum samples collected prior to each infusion. A linear mixed model was conducted to analyze factors that influence trough levels. RESULTS 26 pediatric-onset IBD patients (14 ulcerative colitis (UC), 9 Crohn's disease (CD), 3 IBD-unclassified) received 258 vedolizumab infusions. Mean vedolizumab trough level at week 6 was 29.9 μg/ml (SD 17.8), and 11.5 μg/ml (SD 4.9) during maintenance therapy. CD patients had significantly lower trough levels than UC/IBD-U patients (β 15.2; 95%CI -1.1- 29.2; p = 0.036). Higher fecal calprotectin (β -0.009; 95%CI -0.02- -0.003; p = 0.007) and C-reactive protein levels (β -0.4; 95%CI -0.72- -0.04; p = 0.027) were associated with lower trough levels, whereas shortening of time between infusions led to higher trough levels (β -0.77, 95%CI-0.9 - 0.64; p < 0.001). CONCLUSIONS In this group of pediatric-onset IBD patients trough levels were significantly lower in CD patients compared to UC/IBD-U patients. Higher levels of inflammatory markers were associated with lower vedolizumab trough levels.