Michael D. Kappelman

INTRODUCTION: Obesity is common among patients with pediatric Crohn's disease (PCD). Some adult studies suggest obese patients respond less well to anti-tumor necrosis factor (TNF) treatment. This study sought compares anti-TNF response and anti-TNF levels between pediatric patients with normal and high body mass index (BMI). METHODS: The COMBINE trial compared anti-TNF monotherapy with combination therapy with methotrexate in patients with PCD. In this secondary analysis, a comparison of time-to-treatment failure among patients with normal BMI vs BMI Z -score >1, adjusting for prescribed anti-TNF (infliximab [IFX] or adalimumab [ADA]), trial treatment assignment (combination vs monotherapy), and relevant covariates. Median anti-TNF levels across BMI category was also examined. RESULTS: Of 224 participants (162 IFX initiators and 62 ADA initiators), 111 (81%) had a normal BMI and 43 (19%) had a high BMI. High BMI was associated with treatment failure among ADA initiators (7/10 [70%] vs 12/52 [23%], hazard ratio 0.29, P = 0.007) but not IFX initiators. In addition, ADA-treated patients with a high BMI had lower ADA levels compared with those with normal BMI (median 5.8 vs 12.8 μg/mL, P = 0.02). IFX trough levels did not differ between BMI groups. DISCUSSION: Overweight and obese patients with PCD are more likely to experience ADA treatment failure than those with normal BMI. Higher BMI was associated with lower drug trough levels. Standard ADA dosing may be insufficient for overweight children with PCD. Among IFX initiators, there was no observed difference in clinical outcomes or drug levels, perhaps due to weight-based dosing and/or greater use of proactive drug monitoring.