Prenatal prescription of macrolide antibiotics and infantile hypertrophic pyloric stenosis.

OBJECTIVE: To assess the association between prenatal antibiotics, including erythromycin, and infantile hypertrophic pyloric stenosis in a large cohort of infants.
METHODS: This was a retrospective cohort study of births to women enrolled in Tennessee Medicaid/TennCare, 1985-1997. Prescriptions for erythromycin, nonerythromycin macrolides, and other antibiotics were identified from pharmacy files linked with birth certificate files. The primary study outcome was development of pyloric stenosis in the infant, identified from linked hospital discharge diagnosis and surgical procedure codes.
RESULTS: The cohort included 260,799 mother/infant pairs. Among these women, 13,146 filled prescriptions for erythromycin (50.4 per 1000), and 621 filled prescriptions for nonerythromycin macrolides (2.4 per 1000). There was no association with prenatal erythromycin prescription and infantile hypertrophic pyloric stenosis either after 32 weeks' gestation (adjusted odds ratio 1.17, 95% confidence interval, 0.84, 1.64, P =.33) or at any time during pregnancy (adjusted odds ratio 1.15, 95% confidence interval 0.84, 1.56, P =.36). There was an association between maternal prescriptions for nonerythromycin macrolides and infantile hypertrophic pyloric stenosis (adjusted odds ratio 2.77, 95% confidence interval 1.22, 6.30, P =.01).
CONCLUSION: The hypothesized association between erythromycin and infantile pyloric stenosis was not seen. Causal inference from the association between prenatal nonerythromycin macrolides and infantile hypertrophic pyloric stenosis is limited by the small number of affected children and the evidence of other differences between users of nonerythromycin macrolides and controls.