Oseltamivir and its active metabolite, oseltamivir carboxylate, are excreted into human breast milk in very small amounts.  Limited data suggest that clinical sequelae from maternal treatment would not be expected in a breastfed infant.

There are no data on zanamivir use during lactation but based on limited bioavailability the systemic exposure of a breastfed infant from maternal treatment is expected to be insignificant.

The overall consensus is that treatment with either drug is not a reason to discontinue, or put limitations on, breastfeeding full-term or pre-term infants.  Due to the very small amounts transferred into breast milk, and the limited oral bioavailability of either drug, the benefits of breastfeeding are considered to outweigh any, albeit unidentified, risks.

If an infant being breastfed by the mother receiving oseltamivir or zanamivir needs direct treatment or chemoprophylaxis, the recommended dose of oseltamivir or zanamivir for infants should be given.