Antiviral agent used for topical treatment of herpes of the lip. Famciclovir is its precursor drug which is used for systemic treatment. At latest update, relevant published data on excretion into breast milk were not found. After topical use, plasma levels are undetectable. Such property is the main reason by which it is not excreted into breast milk, In addition, a low oral bioavailability would impede the absorption from ingested milk toward the infant's plasma. Do not apply creams, gels and other products for topical use that would contain paraffin (mineral oil) on the breast to prevent ingestion by the infant. If necessary, apply Penciclovir after a feed and clean thoroughly with water before the next.