Procaine Penicillin G

Drug Levels and Effects:

Summary of Use during Lactation:

ProcainepenicillinGis acceptable to use during breastfeeding. Amounts ingested by the infant are small and would not be expected to cause any adverse effects. Occasionally, disruption of the infant's gastrointestinal flora, resulting in diarrhea or thrush, has been reported withpenicillins, but these effects have not been adequately evaluated.

Drug Levels:

Maternal Levels.

No studies have reported milkpenicillinGlevels after administration ofprocainepenicillinGto the mother.[1] However, after 2 doses of 2 million units of aqueouspenicillinGintramuscularly in 15 women, peak milk levels were 120 units/L and trough levels were 10 units/L. Two women received 2.4 million units ofbenzathinepenicillinGintramuscularly 20 hours after delivery. Milk concentrations decreased from 30 units/L on the third day to 10 units/L on the fifth day. After the fifth day, milk levels were undetectable.[2] Milk levels after 2 to 2.4 million units ofprocainepenicillinGwould be expected to be between those of similar doses of aqueous andbenzathinepenicillinG.

Infant Levels.

Relevant published information was not found as of the revision date.

Effects in Breastfed Infants:

A breastfed 1-month-old infant with congenital syphilis developed a Herxheimer reaction 6 hours after its mother received 2.4 million units ofbenzathinepenicillinGintramuscularly. However, the baby had also received 10 units ofpenicillinGat about the same time as the mother's injection. The reaction was possibly caused bypenicillinin breastmilk.[3]

Possible Effects on Lactation:

Relevant published information was not found as of the revision date.


1. Rozansky R, Brzezinsky A. The excretion ofpenicillinin human milk. J Lab Clin Med. 1949;34:497-500.
2. Borderon E, Soutoul JH et al. [Excretion of antibiotics in human milk]. Med Mal Infect. 1975;5:373-6.
3. Rollier R, Rollier M, Bellouchi M. [Herxheimer's reaction in maternal milk in early congenital syphilis.] Bull Soc Fr Dermatol Syphiligr 1967;74:178-80. PMID:6070262

Substance Identification:

Substance Name:


CAS Registry Number:


Drug Class:

  • Antiinfective Agents

  • Antibacterial Agents

  • Penicillins

    Administrative Information:

    LactMed Record Number:


    Last Revision Date:

    Disclaimer:Information presented in this database is not meant as a substitute for professional judgment. You should consult your healthcare provider for breastfeeding advice related to your particular situation. The U.S. government does not warrant or assume any liability or responsibility for the accuracy or completeness of the information on this Site.