Ondansetron (Zofran) is safe for treatment of nausea in pregnancy

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1. Treatment of nausea and vomiting in pregnancy with ondansetron was not associated with an increased risk of major birth defects, spontaneous abortion, still birth, preterm delivery, or low birth weight/small for gestational age infants. 

2. Lower rates of spontaneous abortion are seen in women exposed to ondansetron and/or other antiemetic antihistamines; however, it is nausea and vomiting that are associated with a lower risk of spontaneous abortion, not the medications.

In a study published today, ondansetron exposure was not associated with a significant increase in the risk of spontaneous abortion, stillbirth, any major birth defects, preterm delivery, low birth weight or small for gestational age infants in this retrospective propensity-score matched analysis.

More than half of all women are affected by nausea and vomiting during pregnancy and 10-15% of women have symptoms severe enough to warrant drug treatment. Typically, nausea starts between 3 and 8 weeks of gestation and peaks around 7-12 weeks, which corresponds to the most vulnerable period in fetal development. The antiemetic ondansetron, a selective 5-HT3-receptor antagonist, has become one of the most common medications prescribed during pregnancy despite limited data on safety.

Prior to adjustment, the risk of spontaneous abortion was significantly reduced in women exposed to ondansetron. Further analysis showed that nausea and vomiting, not ondansetron or other antiemetic exposure, were associated with a lower risk of spontaneous abortion. Regarding prior work on adverse outcomes, a 2012 case-control study assocated ondansetron use with increased risk of cleft palate. The current study analyzed birth defects in aggregate and was not powered to detect individual defects. So, while this study provides reassurance that ondansetron is safe for treatment of nausea and vomiting in pregnancy, it cannot rule out the possibility of adverse effects. 

Click to read the study in NEJM

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1. Treatment of nausea and vomiting in pregnancy with ondansetron was not associated with an increased risk of major birth defects, spontaneous abortion, still birth, preterm delivery, or low birth weight/small for gestational age infants.  

2. Lower rates of spontaneous abortion are seen in women exposed to ondansetron and/or other antiemetic antihistamines; however, it is nausea and vomiting that are associated with a lower risk of spontaneous abortion, not the medications.

This [registry-based cohort] study, based in Denmark, analyzed pregnancy outcomes associated with exposure to ondansetron in all pregnancies resulting in a singleton live birth, stillbirth, or ending with any abortive outcome. Pregnancies with exposure to ondansetron prior to 6 weeks, known chromosomal abnormalities, exposure to known causes of birth defects, and fetal loss prior to 6 weeks were excluded, resulting in an initial cohort of 608,385 patients with exposure to ondansetron in 1970 pregnancies. In all analyses, women exposed to ondansetron were matched 1:4 to unexposed women.  Patients exposed to ondansetron were grouped according to timing of exposure and the analysis of adverse outcome pregnancies was matched to unexposed women by propensity-score analysis. Ondansetron exposure was not associated with a significant increase in the risk of adverse outcomes. Additionally, the study showed a protective effect of nausea and vomiting against spontaneous abortion.

In sum: Ondansetron exposure was not associated with a significant increase in the risk of spontaneous abortion, stillbirth, any major birth defects, preterm delivery, low birth weight or small for gestational age infants in this retrospective propensity-score matched analysis.

More than half of all women are affected by nausea and vomiting during pregnancy and 10-15% of women have symptoms severe enough to warrant drug treatment. Typically, nausea starts between 3 and 8 weeks of gestation and peaks around 7-12 weeks, which corresponds to the most vulnerable period in fetal development. The antiemetic ondansetron, a selective 5-HT3-receptor antagonist, has become one of the most common medications prescribed during pregnancy despite limited data on safety.

Prior to adjustment, the risk of spontaneous abortion was significantly reduced in women exposed to ondansetron. Further analysis showed that nausea and vomiting, not ondansetron or other antiemetic exposure, were associated with a lower risk of spontaneous abortion. Regarding prior work on adverse outcomes, a 2012 case-control study assocated ondansetron use with increased risk of cleft palate. The current study analyzed birth defects in aggregate and was not powered to detect individual defects. So, while this study provides reassurance that ondansetron is safe for treatment of nausea and vomiting in pregnancy, it cannot rule out the possibility of adverse effects. 

Click to read the study in NEJM

By Jessica Mitchell and Mitalee Patil

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