Because of the low levels of azithromycin in breastmilk and use in infants in higher doses, it would not be expected to cause adverse effects in breastfed infants. Monitor the infant for possible effects on the gastrointestinal flora, such as vomiting, diarrhea, candidiasis (thrush, diaper rash). Unconfirmed epidemiologic evidence indicates that the risk of infantile hypertrophic pyloric stenosis might be increased by maternal use of macrolide antibiotics during the first two weeks of breastfeeding, but others have questioned this relationship. In one study, a single dose of azithromycin given during labor to women who were nasal carriers of pathogenic Staphylococcus and Streptococcus reduced the counts of these bacteria in breastmilk, but increased the prevalence of azithromycin-resistant E. coli and K. pneumoniae in breastmilk.