title: Effect of long-term antibiotic use on weight in adolescents with acne.
abstract: OBJECTIVE
  Antibiotics increase weight in farm animals and may cause weight gain in humans. We used electronic health records from a large primary care organization to determine the effect of antibiotics on weight and BMI in healthy adolescents with acne.
  
  
  METHODS
  We performed a retrospective cohort study of adolescents with acne prescribed ≥4 weeks of oral antibiotics with weight measurements within 18 months pre-antibiotics and 12 months post-antibiotics. We compared within-individual changes in weight-for-age Z-scores (WAZs) and BMI-for-age Z-scores (BMIZs). We used: (i) paired t-tests to analyse changes between the last pre-antibiotics versus the first post-antibiotic measurements; (ii) piecewise-constant-mixed models to capture changes between mean measurements pre- versus post-antibiotics; (iii) piecewise-linear-mixed models to capture changes in trajectory slopes pre- versus post-antibiotics; and (iv) χ(2) tests to compare proportions of adolescents with ≥0.2 Z-scores WAZ or BMIZ increase or decrease.
  
  
  RESULTS
  Our cohort included 1012 adolescents with WAZs; 542 also had BMIZs. WAZs decreased post-antibiotics in all analyses [change between last WAZ pre-antibiotics versus first WAZ post-antibiotics = -0.041 Z-scores (P < 0.001); change between mean WAZ pre- versus post-antibiotics = -0.050 Z-scores (P < 0.001); change in WAZ trajectory slopes pre- versus post-antibiotics = -0.025 Z-scores/6 months (P = 0.002)]. More adolescents had a WAZ decrease post-antibiotics ≥0.2 Z-scores than an increase (26% versus 18%; P < 0.001). Trends were similar, though not statistically significant, for BMIZ changes.
  
  
  CONCLUSIONS
  Contrary to original expectations, long-term antibiotic use in healthy adolescents with acne was not associated with weight gain. This finding, which was consistent across all analyses, does not support a weight-promoting effect of antibiotics in adolescents.
authors.affiliation: Division of Infectious Diseases, Department of Pediatrics, Stanford University School of Medicine, Stanford, CA 94305, USA Palo Alto Medical Foundation Research Institute, Palo Alto, CA 94301, USA dcontop@stanford.edu.
authors.forename: Despina G
authors.initials: DG
authors.lastname: Contopoulos-Ioannidis
authors.affiliation: Division of Infectious Diseases and Geographic Medicine, Department of Medicine, Stanford University School of Medicine, Stanford, CA 94305, USA.
authors.forename: Catherine
authors.initials: C
authors.lastname: Ley
authors.affiliation: Palo Alto Medical Foundation Research Institute, Palo Alto, CA 94301, USA.
authors.forename: Wei
authors.initials: W
authors.lastname: Wang
authors.affiliation: Division of Infectious Diseases and Geographic Medicine, Department of Medicine, Stanford University School of Medicine, Stanford, CA 94305, USA.
authors.forename: Ting
authors.initials: T
authors.lastname: Ma
authors.affiliation: Palo Alto Medical Foundation Research Institute, Palo Alto, CA 94301, USA.
authors.forename: Clifford
authors.initials: C
authors.lastname: Olson
authors.affiliation: Palo Alto Medical Foundation Research Institute, Palo Alto, CA 94301, USA.
authors.forename: Xiaoli
authors.initials: X
authors.lastname: Shi
authors.affiliation: Palo Alto Medical Foundation Research Institute, Palo Alto, CA 94301, USA.
authors.forename: Harold S
authors.initials: HS
authors.lastname: Luft
authors.affiliation: Department of Statistics, Stanford University School of Humanities and Sciences and Department of Health Research and Policy, Stanford University School of Medicine, Stanford, CA 94305, USA.
authors.forename: Trevor
authors.initials: T
authors.lastname: Hastie
authors.affiliation: Division of Infectious Diseases and Geographic Medicine, Department of Medicine, Stanford University School of Medicine, Stanford, CA 94305, USA Department of Health Research and Policy, Stanford University School of Medicine, Stanford, CA 94305, USA.
authors.forename: Julie
authors.initials: J
authors.lastname: Parsonnet
mesh_terms: D000152:Acne Vulgaris / Q000453:epidemiology*; D000293:Adolescent; D000328:Adult; D000900:Anti-Bacterial Agents / Q000008:administration & dosage / Q000009:adverse effects* / Q000627:therapeutic use; D001835:Body Weight / Q000187:drug effects*; D002648:Child; D005260:Female; D006801:Humans; D008297:Male; D015233:Models, Statistical; D012189:Retrospective Studies; D055815:Young Adult
chemical_list: D000900:Anti-Bacterial Agents