At latest update on excretion into breast milk of Penicillin procaine published information was not found. Mother plasma levels of Penicillin procaine have been shown to be lower than those of Penicillin G. Penicillin G is excreted into breast milk in non-significant amounts without side-effects observed among breastfed infants from treated mothers. Plasma levels in those infants were shown to be low or undetectable. Penicillin is a broad spectrum antibiotic that is commonly used in Pediatrics and Neonatology with very good tolerance even in premature newborns. Be aware of false negative results that may be obtained from infants with bacterial cultures when the mother is on antibiotics. Eleventh WHO's Model List of Essential Drugs 2002: Compatible with breastfeeding.