Body mass index of children at risk for urinary tract infections: secondary analysis of the RIVUR trial
Thomas Gaither, BS1, Christopher Cooper, MD2, Zachary Kornberg, BS1, Laurence Baskin, MD1, Hillary Copp, MD, MS1.
1University of California, San Francisco, San Francisco, CA, USA, 2University of Iowa, Iowa City, IA, USA.
Continuous antibiotic prophylaxis (CAP) has been a long-standing management strategy in patients with vesicoureteral reflux (VUR). Although the benefits of CAP were evaluated in the Randomized Intervention for Children with Vesicoureteral Reflux (RIVUR) trial, the potential downsides of CAP are still being elucidated. In particular, the impact CAP has on body mass index (BMI), a surrogate marker for obesity, is unknown. Previous studies have shown that antibiotic exposure in young infants causes weight gain.
Materials & Methods
We conducted a secondary analysis of the RIVUR trial. BMI was recorded at each visit during the trial and was converted to percentile scores based on sex, age, and height. We used generalized estimating equations to account for longitudinal data and used treatment assignment (TMP-SMX versus placebo) as our sole predictor. We tested whether the effects of CAP on BMI percentile differed by bladder and bowel dysfunction (BBD) and dilating reflux (grades 3-5) diagnosed at baseline and at end of study follow-up.
The median (interquartile range, IQR) baseline BMI percentile in all patients at baseline was 63 (36-85). The median (IQR) BMI percentile at latest follow-up was 66 (34-85). During the study period, patients on CAP decreased BMI percentiles by 3.9% (95% confidence interval, CI -0.1-7.9, p=0.06). The effects of CAP on change of BMI percentile did not differ by baseline BBD status (4.2, 95%CI -14.8-23.2, p=0.66) or follow-up BBD status (-1.3, 95%CI -13.0-10.4, p=0.83). The effects of CAP on change of BMI percentile did not differ by dilating versus non-dilating VUR status at baseline (-2.3, 95%CI -10.3-5.7, p=0.57). However, patients with dilating reflux at follow-up that were treated with CAP increased BMI percentile by 13.1 (95%CI 0.4-25.7, p=0.04) when compared to those with non-dilating reflux at follow-up treated with placebo.
CAP was associated with decreased BMI percentiles. The effect of CAP may be more in those patients adherent to CAP as non-adherence biases our effect estimates toward the null. Baseline clinical characteristics did not change the effect CAP has on BMI. CAP was associated with a significant increase in BMI in children with persistent dilating reflux, although the mechanism for this remains unclear.
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