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Ondansetron (a 5-hydroxytryptamine type 3 receptor antagonist) is often used off-label to treat nausea and vomiting during pregnancy (NVP), but fetal safety data are limited. In a retrospective cohort study, Danish investigators used national registry data to assess the effects of this medication on risk for adverse outcomes in all singleton pregnancies from 2004 (when ondansetron was first commonly used for NVP in Denmark) to 2011. Each woman who had received ondansetron was matched with four unexposed women. Analyses to account for potential confounders included adjustment for hospitalization for NVP and exposure to antiemetics other than ondansetron. Ondansetron was prescribed for 1970 of 608,385 pregnancies. Median gestational age at first dose was 10 weeks; median number of doses per pregnancy was 30.
Compared with unexposed women, those who received ondansetron did not have significantly elevated risk for spontaneous abortion (hazard ratio at 7–12 weeks' gestation, 0.5; HR at 13–22 weeks' gestation, 0.6), stillbirth (HR, 0.4), infant with major birth defect (prevalence odds ratio, 1.1), preterm delivery (POR, 0.9), delivery of a low-birth-weight infant (POR, 0.8), or delivery of a small-for-gestational-age infant (POR, 1.1). Risks for adverse fetal outcomes were similar among women who filled single or multiple prescriptions for ondansetron.
Pasternak B et al. Ondansetron in pregnancy and risk of adverse fetal outcomes. N Engl J Med 2013 Feb 28; 368:814. (http://dx.doi.org/10.1056/NEJMoa1211035)
Comment
Ondansetron often provides relief from nausea and vomiting during pregnancy when other treatments have failed. Previous studies have shown that NVP is associated with lower risk for spontaneous abortion. The authors' findings that exposure to antihistamines (often used as first-line treatment for NVP) — as well as to ondansetron — was associated with reduced spontaneous abortion risk support the conclusion that NVP itself, rather than its treatment, lowers risk for spontaneous abortion. Furthermore, this large, well-executed study provides reassurance about the fetal safety of ondansetron use during pregnancy.