Benzathine penicillin G

Drug Levels and Effects:

Summary of Use during Lactation:

BenzathinepenicillinGis acceptable to use during breastfeeding. Limited information indicates that single maternal doses ofbenzathinepenicillinGof 2.4 million units intramuscularly produce low levels in milk that are not expected to cause adverse effects in breastfed infants. 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.

Two women received one dose of 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. The authors estimated that an exclusively breastfed infant would receive a maximum of 6 to 7 units daily.[1]

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.[2]

Possible Effects on Lactation:

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


1. Borderon E, Soutoul JH et al. [Excretion of antibiotics in human milk]. Med Mal Infect. 1975; 5:373-6.
2. 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:

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