University of Otago public health researcher Dr Sarah Donald said her study has found the use of ondansetron had increased from almost no use (0.1%) in 2005, to 9.1% in 2019.
However, the medicine had not been approved to treat nausea in pregnancy, and such use was considered ‘‘off label’’.
‘‘Most clinical guidelines from the study period recommended ondansetron only if other anti-nausea medicines had been ineffective.
‘‘But what we saw was, over time, its use as a first-line treatment also increased.
‘‘Loosening of prescribing restrictions over time, and the fact that it comes in an easy-to-take dissolvable tablet, have probably contributed to its rising popularity for treating nausea in pregnancy.
‘‘Newer guidelines now recommend ondansetron as one option for first-line treatment in those with moderately severe symptoms.’’
Dr Donald said anti-nausea medication use during pregnancy had increased five-fold between 2005 and 2019, from 4.1% to almost 20%.
The research used anonymised national health data to review prescribing in 1.37 million pregnancies over that timeframe.
Nausea and vomiting during pregnancy were very common, but the substantial impact they had on affected women had historically been under-recognised and under-treated, she said.
However, she was surprised by how quickly the use of ondansetron had become common during pregnancies in New Zealand.
Ondansetron is a very effective anti-nausea medicine that was developed for treating nausea caused by cancer treatments.
Dr Donald said nausea and vomiting in pregnancy affected up to 70% of pregnancies and, as with any medicine used during pregnancy, the safety of anti-nausea medicines needed to be considered.
Several previous studies suggested ondansetron exposure during the first trimester may be associated with a very small increase in the risk of birth defects, such as heart defects and cleft lip/palate.
However, other studies had not found increased risk.
She said the evidence overall, was ‘‘unclear’’.
‘‘I think most of the evidence suggests that it doesn’t represent a huge safety issue.
‘‘But they haven’t been able to rule out a very small increased risk.
‘‘And if the use of ondansetron becomes more and more and more, then even with a very small risk it could be that there’s an increased number of babies that would be affected.
‘‘There just isn’t enough information to say with any certainty either way.
‘‘So I think we need more information before we can say either way.’’
The research team is now investigating whether early-pregnancy ondansetron use is associated with several adverse pregnancy outcomes.
Until the research was completed, she recommended people keep using ondansetron.
‘‘I don’t want to cause a panic or anything like that.’’
