Weight Gain and Obesity in Infants and Young Children Exposed to Prolonged Antibiotic Prophylaxis

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An association between antibiotic use and excessive weight gain or obesity in healthy infants and young children has been reported, but evidence is inconsistent and based on observational studies of growth in relation to incidental antibiotic exposures.


To evaluate whether prolonged antibiotic exposure is associated with weight gain in children participating in a clinical trial of antibiotic prophylaxis to prevent recurrent urinary tract infection.

Design, Setting, and Participants

Secondary analysis of data from the Randomized Intervention for Children With Vesicoureteral Reflux Study, a 2-year randomized clinical trial that enrolled participants from 2007 to 2011. All 607 children who were randomized to receive antibiotic (n = 302) or placebo (n = 305) were included. Children with urinary tract anomalies, premature birth, or major comorbidities were excluded from participation.


Trimethoprim-sulfamethoxazole or placebo taken orally, once daily, for 2 years.

Main Outcomes and Measures

Weight gain as measured by change in weight-for-age z score from baseline to the end-of-study visit at 24 months. Secondary outcomes included weight gain at 6, 12, and 18 months and the prevalence of overweight or obesity at 24 months.


Participants had a median age of 12 months (range, 2-71 months) and 558 of 607 (91.9%) were female. Anthropometric data were complete at the 24-month visit for 428 children (214 in the trimethoprim-sulfamethoxazole group and 214 in the placebo group). Weight gain in the trimethoprim-sulfamethoxazole group and the placebo group was similar (mean [SD] change in weight-for-age z score: +0.14 [0.83] and +0.18 [0.85], respectively; difference, −0.04 [95% CI, −0.19 to 0.12]; P = .65). There was no significant difference in weight gain at 6, 12, or 18 months or in the prevalence of overweight or obesity at 24 months (24.8% vs 25.7%; P = .82). Subgroup analyses showed no significant interaction between weight gain effect and age, sex, history of breastfeeding, prior antibiotic use, adherence to study medication, or development of urinary tract infection during the study.

Conclusions and Relevance

Based on a secondary analysis of data from a large clinical trial of trimethoprim-sulfamethoxazole prophylaxis, there was no evidence that prolonged exposure to this antibiotic has a concurrent effect on weight gain or the prevalence of overweight or obesity in healthy infants and young children.

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