Ondansetron and pregnancy: Understanding the data

Nausea and vomiting of pregnancy (NVP) is a common condition affecting 75% of pregnant women. NVP generally commences early in the first trimester, peaking in severity between 7 and 12 weeks and in over 90% symptoms will have abated by week 20. Thus, the time when women are most likely to have NVP and require treatment coincides with the embryonic period when there is maximum susceptibility to any teratogenic risk. Following the thalidomide tragedy of 55 years ago there is a particular awareness and sensitivity about these potential risks, especially in relation to any medication used to treat NVP. Despite several studies showing no clear benefits of ondansetron over other NVP treatments such as doxylamine, and the paucity of safety data, the off-label prescribing and use of ondansetron to treat NVP has increased significantly worldwide. Albeit based on limited human pregnancy data, ondansetron has not been associated with a significantly increased risk of birth defects or other adverse pregnancy outcomes. This review attempts to highlight some of the difficulties in interpreting the available data and the need to follow practical guidelines regarding treatment of NVP.