Clarithromycin reaches a discrete concentration into breast milk, so it can be considered acceptable for use in nursing mothers. It is estimated that a baby can get to ingest up to 2% of the dose given to the mother.
No relevant adverse effects are expected in the baby, although the substance may cause gastrointestinal disturbances such as anal or oral thrush, diarrhea and rashes.
An observational study concludes that there is an increased risk of hypertrophic pyloric stenosis in infants whose mothers had received a macrolide. Less than 2% of mothers had received clarithromycin.
Warning of the manufacturer:
It has not been established clarithromycin safety during lactation.
Clarithromycin is excreted in breast milk, so it should not be used during lactation.