Drug levels of VEDOLIZUMAB in patients with pediatric-onset inflammatory bowel disease in a real-life setting.

Vedolizumab (VDZ) is used off-label in pediatric inflammatory bowel disease (PIBD). There are less data on drug levels to achieve and maintain remission in children. We aimed to study vedolizumab (VDZ) trough levels in a pediatric population in a real-life setting. We traced 50 patients with PIBD receiving VDZ treatment at our hospital, reviewed their treatment protocol, trough levels, and antidrug antibodies, and compared those to fecal calprotectin (FC) levels and achievement of corticosteroid-free maintenance therapy (CF). VDZ trough level was available from 198 samples during a median follow- up of 12.6 months. Proceeding to maintenance therapy was associated with a decline in FC but not with VDZ trough levels that were comparable between patients with FC < 100 μg/g (remission), 100-1000 μg/g, or > 1000 μg/g at 3 months (mean levels of 36.8, 28.6, and 27 μg/mL, respectively p = 0.188). At 3 months, patients achieving CF (41%) and those on corticosteroids had comparable VDZ trough levels (33 vs. 27.5 μg/mL, respectively). At 6 months, the trough level was similar in groups with FC < 100 μg/g or FC > 1000 μg/g (31.5 and 27.6 μg/mL, p = 0.859). Treatment intensification did not improve the achieved CF at 12 months. None developed drug antibodies nor discontinued the therapy for an adverse event.   Conclusion: VDZ was a well-tolerated and safe biologic treatment. A positive response on gut inflammation after induction predicted proceeding to maintenance therapy whereas trough levels did not. A VDZ trough level associated with clinical remission or continuing with VDZ treatment could not be determined. What is Known: • In pediatric inflammatory bowel disease, vedolizumab is still in off-label use. • The results on the relationship between drug levels of vedolizumab and clinical remission in pediatric patients are contradictory. What is New: • This real-life setting in pediatric-onset inflammatory bowel disease showed no benefit of therapy enhancement during a median follow-up of one year. • Trough levels of vedolizumab were not associated with therapy outcomes.