Ondansetron (Zofran) Safety During Breastfeeding a 2-Month-Old
Ondansetron is compatible with breastfeeding and can be used safely by mothers nursing a 2-month-old infant, with no need to interrupt breastfeeding or discard breast milk. 1
Evidence-Based Safety Profile
Transfer into Breast Milk
- Ondansetron transfers into breast milk in minimal amounts, with a predicted relative infant dose of only 3.0% of the maternal weight-adjusted dose, which is well below the 10% safety threshold used to assess medication compatibility with breastfeeding 2
- The calculated daily infant exposure is approximately 0.005 mg/kg/day, which represents an extremely low dose 2
- Due to ondansetron's poor oral bioavailability and extensive first-pass hepatic metabolism, the actual systemic absorption by the infant from breast milk is even lower than these already minimal amounts 3
Clinical Guidelines Support Use
- The Association of Anaesthetists explicitly states that ondansetron is compatible with breastfeeding, though they note there are no direct human studies on transfer into breast milk (only animal data) 3
- Multiple clinical practice guidelines recommend ondansetron as a safe anti-emetic option for breastfeeding mothers, including those from the American College of Obstetricians and Gynecologists 1
- Ondansetron is listed alongside other compatible anti-emetics (granisetron, cyclizine, prochlorperazine, dexamethasone, metoclopramide, and domperidone) as safe options for nursing mothers 1
Practical Clinical Recommendations
Timing and Administration
- No waiting period is required after taking ondansetron - mothers can breastfeed immediately without needing to pump and discard milk 1
- There is no need to time breastfeeding around medication doses, as the transfer is minimal regardless of timing 3, 1
Special Considerations for Young Infants
- While extra caution is generally advised for infants less than 6 weeks of age due to immature hepatic and renal function, the extremely low transfer of ondansetron into breast milk makes it safe even for younger infants 1
- At 2 months of age, your infant has more mature drug metabolism than a newborn, further reducing any theoretical concerns 1
Important Safety Caveat
- If the mother co-sleeps with her infant, she should avoid doing so immediately after taking ondansetron if she experiences any sedation, as her natural responsiveness may be temporarily reduced 1, 4
- However, ondansetron typically causes minimal sedation compared to other anti-emetics 3
Supporting Evidence from Clinical Use
Real-World Safety Data
- A prospective study of 176 pregnant women exposed to ondansetron showed no increased risk of major malformations (3.6% rate, which is within baseline), demonstrating safety during pregnancy 5
- Case reports document safe use of ondansetron throughout all trimesters of pregnancy with no adverse effects on mother or infant 6
- The drug has been extensively studied in children for gastroenteritis-related vomiting, with a very low risk of adverse effects 7
Cardiac Safety Note
- The FDA warning about QT prolongation applies specifically to the 32 mg IV dose used in cancer chemotherapy, not the lower doses (typically 4-8 mg) used for nausea and vomiting in other settings 8
- Standard doses for nausea (4-8 mg) have not been associated with clinically significant cardiac risks in breastfeeding mothers 8
Bottom Line
Mothers taking ondansetron for nausea or vomiting can continue breastfeeding their 2-month-old infant without any restrictions, interruptions, or concerns about infant safety. The evidence consistently demonstrates minimal drug transfer, extensive first-pass metabolism limiting infant absorption, and a relative infant dose well below safety thresholds. 3, 1, 2