Is Ondansetron safe while breastfeeding?

Summary of use during breastfeeding

Ondansetron is frequently used for nausea during and after cesarean section, usually in doses of 4 to 8 mg intravenously.[1-4] Use during and after cesarean section appears to not affect the onset of breastfeeding.[1,5] No adverse infant effects have been reported in this setting or among women who received ondansetron postpartum in a pharmacokinetic study. Use of ondansetron in nursing mothers beyond the immediate postpartum setting has not been studied well, but the drug is labeled for use in infants as young as 1 month of age. A computer model demonstrated that the amounts in milk are much less than this dose. No special precautions are required.

Effects on the breastfed infant

In a pharmacokinetic study of 78 women who received ondansetron intravenously postpartum, no adverse effects were reported in their breastfed infants.[6]

Effects on milk supply

A randomized, double-blind study compared placebo to intravenous ondansetron 4 mg given after cesarean section as prophylaxis for postoperative nausea and vomiting. There was no difference in the time of the first breastfeeding between the two groups.[3]

In a retrospective study of women undergoing cesarean section deliveries, 3 regimens were compared: dexmedetomidine before anesthesia and during delivery (n = 115), normal saline before anesthesia and during delivery and dexmedetomidine after delivery (n = 109), and normal saline before anesthesia and during delivery (n = 168). All women received ondansetron 4 mg as needed and before removal of sutures. The average total amount of ondansetron consumed in the women ranged from 6 mg to 9 mg in the various groups. The time to first production of milk was similar in all groups (25 to 28 minutes).[5]

Levels in milk

Maternal Levels. A pharmacokinetic study was performed using opportunistic sampling of a convenience sample of 78 lactating women receiving intravenous ondansetron for the treatment of post-operative nausea and vomiting in a median dose of ondansetron of 4 mg (range 4 to 8 mg). The 78 women included in the analysis contributed a total of 67 plasma samples and 53 usable milk samples. Using the average milk concentration over 24 hours, the daily infant dose was estimated to be 0.002 mg/kg and the RID was 3.7% of a weight-adjusted single maternal dose of 4 mg. These data were used to build a computer model to simulate ondansetron levels in breastmilk. After optimizing the model, the median peak milk concentration was predicted to be 20.2 mcg/L at 0.5 hours after a 4 mg intravenous dose at 2 days postpartum. The estimated daily infant dosage was 5 mcg/kg, which translated into a relative infant dose of 3.3% of the maternal weight-adjusted dosage and was 1.6% of the standard dosage given to infants.[6]

Infant Levels. A pharmacokinetic study was performed using opportunistic sampling of a convenience sample of 78 lactating women receiving intravenous ondansetron for the treatment of post-operative nausea and vomiting in a median dose of ondansetron of 4 mg (range 4 to 8 mg). Among the 20 infant plasma samples that were collected, 7 were below the limit of quantification. Among the 13 infants with a quantifiable plasma concentration, the median concentration was 0.78 mcg/L (range 0 to 7.2) mcg/L. The highest observed concentration among these 13 infants was approximately 10% of the median peak concentration (76.6 mcg/L) observed in an open-label, single-dose pharmacokinetic study conducted in pediatric surgical patients aged 1 to 24 months who received a single 0.1 mg/kg dose of intravenous ondansetron.[6]

Ondansetron in pregnancy

LactMed covers breastfeeding only. For what the NHS and the US prescribing label say about pregnancy, see:

• Is ondansetron safe in pregnancy and breastfeeding?