Fosfomycin and breastfeeding

A recent article on the treatment of resistant urinary tract infections stated that small amounts of fosfomycin are excreted in breast milk so it is not recommended in breastfeeding.¹ Fosfomycin absorption is largely dependent on the salt form – trometamol salts are modestly absorbed (34–58%) and calcium salts are poorly absorbed (<12%). Fosfomycin secreted into human milk would likely be in the calcium form and is unlikely to be absorbed.

Foods and the acidic milieu of the stomach both significantly reduce oral absorption. Concentrations secreted into human milk have been reported to be about 10% of what is present in maternal plasma.^2-6 It is not likely that the amount present in breast milk would produce untoward effects in a breastfeeding infant. On balance fosfomycin may be used with caution.