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Research Letter
November 15, 2019

Intravenous Ondansetron in Pregnancy and Risk of Congenital Malformations

Author Affiliations
  • 1Division of Pharmacoepidemiology and Pharmacoeconomics, Brigham and Women’s Hospital, Boston, Massachusetts
  • 2Department of Epidemiology, Harvard T.H. Chan School of Public Health, Boston, Massachusetts
  • 3Division of Maternal-Fetal Medicine, Brigham and Women’s Hospital, Boston, Massachusetts
JAMA. 2020;323(4):372-374. doi:10.1001/jama.2019.18587

A population-based cohort study previously evaluated the association between first-trimester exposure to the oral formulations of ondansetron and congenital malformations. After accounting for potential confounding variables, there was no significant association with congenital malformations overall or cardiac malformations, but a small increased risk of oral clefts could not be excluded.1 Subsequent research has suggested that intravenous administration of ondansetron may be associated with greater risks of cardiac malformations and oral clefts.2 Potential explanations for the apparent difference in teratogenic effect of intravenous compared with oral formulations include (1) residual confounding by indication and associated factors (eg, nutritional deficiencies) in women with hyperemesis severe enough to require intravenous medication, (2) higher doses administered intravenously vs orally, and (3) higher specificity for exposure because studies of oral use in health care utilization data are based on dispensed medication, and not all women may consume the medication as prescribed. We therefore conducted a follow-up study to examine the association between intravenous ondansetron and congenital malformations.

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