Ondansetron Use in Pregnancy

Introduction to Ondansetron Therapy

• Ondansetron can be used during the first trimester of pregnancy as a second-line antiemetic for severe nausea and vomiting, with the understanding that there is a very small absolute increase in risk of specific birth defects that must be balanced against the significant maternal risks of inadequately treated hyperemesis gravidarum 1, 2

Treatment Algorithm for Nausea and Vomiting in Pregnancy

• The American College of Obstetricians and Gynecologists recommends using ondansetron on a case-by-case basis for persistent symptoms before 10 weeks of pregnancy 1, 3
• Metoclopramide can be used as first-line therapy, with no increased risk of congenital defects reported in meta-analysis of 33,000 first-trimester exposures 1, 2

Safety Evidence and Risk Quantification

• No increased risk of stillbirth, spontaneous abortion, or major birth defects overall 1
• Very small absolute risk increases for specific defects: orofacial clefts (0.03% absolute increase) and ventricular septal defects (0.3% absolute increase) 2

Practical Prescribing Guidance

• Use the lowest effective dose 2
• Administer with methylprednisolone or prednisolone (not dexamethasone or betamethasone) if steroids are needed for chemotherapy-induced nausea 2

Regulatory and Guideline Positions

• The American Gastroenterological Association and European guidelines recommend a step-up approach, using first-line antiemetics before ondansetron 1
• The American College of Obstetricians and Gynecologists recommends case-by-case use of ondansetron before 10 weeks 1, 3