HealthDay News — Early childhood exposure to certain antibiotics, such as penicillin and tetracycline which kill the anaerobic bacteria in the gut, may lead to inflammatory bowel disease (IBD), study findings suggest.

Taking antianaerobic antibiotics was associated with an 84% increased risk for developing IBD, Matthew P. Kronman, MD, MSCE, of Seattle Children’s Hospital, and colleagues reported in Pediatrics.

Risk was highest among children exposed withing the first year of life and decreased with age. Based on current annual antibiotic prescribing rates, an additional 1,700 IBD cases occur in the United States each year that are attributable to antibiotics.

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“Our study suggests that reduction in childhood antianaerobic antibiotic use may have the potential to help curb the rising incidence of childhood IBD,” the researchers wrote.

Kronman and colleagues performed a retrospective analysis on data from 464 UK ambulatory practices that participated in the Health Improvement Network (THIN). The cohort included 1,072,426 children who did not have IBD at baseline and who were followed for at least two years from 1994 to 2009. Overall, 58% of participants were exposed to at least one antianaerobic antibiotic (32% for 1 to 2 weeks and 26% for longer). A total of 748 (0.07%) developed IBS during follow-up.

Antianaerobic antibiotics include penicillin, amoxicillin, ampicillin (Principen), penicillin/b-lactamase inhibitor combinations, tetracyclines, clindamycin (Cleocin), metronidazole (Flagyl), cefoxitin (Mefoxin), carbapenems and oral vancomycin (Vancocin).

The incidence rates of IBD were 0.83 per 10,000 person-years for unexposed children versus 1.52 for exposed children, for an absolute risk increase of 0.69 cases per 10,000 person-years.

While exposure throughout childhood was associated with developing IBD, this relationship decreased with increasing age at exposure. Adjusted hazard ratios were as follows:

  • 5.51 for exposure before the age of 1 year (95% CI: 1.66-18.28)
  • 2.62 by age 5 years (95% CI: 1.61-4.25)
  • 1.57 by age 15  years (95% CI: 1.35-1.84)

Each antibiotic course correlated with a 6% increase in the IBD hazard. There was a dose-response effect noted, with receipt of more than two antibiotic courses more strongly linked to IBD development compared with receipt of one to two courses (adjusted hazard ratios, 4.77 vs. 3.33). Only 1.6% of antibiotics prescribed to children who developed IBS were for gastrointestinal infections.

Study limitations included the use of administrative data, according to the researchers, who pointed out the potential for reverse causality and the misclassification of IBD diagnoses timing. It is possible that some patients in the study may have been prescribed antianaerobic antibiotics to treat undiagnosed IBD, they stated.


  1. Kronman MP et al. Pediatrics. 2012; doi:10.1542/peds.2011-3886.