Ondansetron is a selective 5-HT3 serotonin antagonist used in the treatment of chemotherapy-induced and post-operative nausea and vomiting, and off-licence for nausea and vomiting in pregnancy (NVP) and hyperemesis gravidarum (HG).
The currently available data do not provide evidence that ondansetron use in the first trimester of pregnancy is associated with an increase in the overall malformation rate.
Although small numbers of studies have described statistically significant increased risks of both overall and specific cardiac malformations, namely septal defects, these data are conflicting. Furthermore, most of these studies did not utilise disease-matched ondansetron unexposed control groups, therefore the possibility of confounding cannot be excluded.
Several studies have suggested that associations may exist between maternal ondansetron use and fetal orofacial clefts, specifically cleft palate alone. Whilst the available data are conflicting, should a true association exist, the absolute risk is likely to remain small (background rate ~0.11% vs. ondansetron-exposed rate ~0.14%).
Four studies which utilised data from three unique datasets have also suggested possible associations with overall or specific renal malformations. These observations require further investigation before more definitive conclusions can be drawn.
Studies investigating miscarriage, intrauterine death/stillbirth, low birth weight, preterm delivery and neurodevelopmental impairment risks are more limited than those investigating malformation risks, but do not currently provide evidence suggestive of an increased risk of these outcomes following maternal ondansetron use in pregnancy.
Ondansetron should only be used during pregnancy where the benefits of treatment are considered to outweigh any potential fetal risks. Exposure to ondansetron at any stage in pregnancy would not usually be regarded as medical grounds for termination of pregnancy or any additional fetal monitoring. However, other risk factors may be present in individual cases which may independently increase the risk of adverse pregnancy outcome. Clinicians are reminded of the importance of consideration of such factors when performing case-specific risk assessments.
This is a summary of the full UKTIS monograph for health care professionals and should not be used in isolation. The full UKTIS monograph and access to any hyperlinked related documents is available to NHS health care professionals who are logged in.
If you have a patient with exposure to a drug or chemical and require assistance in making a patient-specific risk assessment, please telephone UKTIS on 0344 892 0909 to discuss the case with a teratology specialist.
If you would like to report a pregnancy to UKTIS please click here to download our pregnancy reporting form. Please encourage all women to complete an online reporting form.