This drug should be used during pregnancy only if clearly needed; it has been used without apparent harmful effects.

AU TGA pregnancy category: A
US FDA pregnancy category: Not assigned.

Risk summary: Malformative risk with use of this drug in pregnant women is unlikely.

Animal studies have failed to reveal evidence of fetal harm. No positive evidence of adverse effects on the fetus observed during human use of penicillins; however, there are no controlled data in human pregnancy.

AU TGA pregnancy category A: Drugs which have been taken by a large number of pregnant women and women of childbearing age without any proven increase in the frequency of malformations or other direct or indirect harmful effects on the fetus having been observed.

US FDA pregnancy category Not Assigned: The US FDA has amended the pregnancy labeling rule for prescription drug products to require labeling that includes a summary of risk, a discussion of the data supporting that summary, and relevant information to help health care providers make prescribing decisions and counsel women about the use of drugs during pregnancy. Pregnancy categories A, B, C, D, and X are being phased out.

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Use is considered acceptable; caution is recommended.
-According to some authorities: Safety has not been established for newborn infants; use is not recommended unless the benefit outweighs the risk.

Excreted into human milk: Yes

Comments:
-The effects in the nursing infant are unknown.
-Limited data indicate that low levels in milk are not expected to cause harmful effects in nursing infants.
-Disruption of infant's gastrointestinal flora (resulting in diarrhea or thrush) reported occasionally with penicillins; such effects have not been adequately evaluated.

No studies have reported milk penicillin G (benzylpenicillin) levels after administration of this drug to the mother. However, after 2 IM doses (2 million units/dose) of aqueous penicillin G in 15 women, peak and trough milk levels were 120 and 10 units/L, respectively. At 20 hours after delivery, 2 women received 2.4 million units of benzathine penicillin G IM; milk levels decreased from 30 units/L on the third day to 10 units/L on the fifth day and were undetectable after the fifth day. Milk levels after 2 to 2.4 million units of this drug would be expected to be between those of similar doses of aqueous and benzathine penicillin G.

A Herxheimer reaction occurred in a 1-month-old breastfed infant with congenital syphilis 6 hours after a 2.4 million-unit IM dose of benzathine penicillin G was administered to the mother; the infant had also received 10 units of penicillin G at about the time of the maternal dose. The reaction was possibly due to penicillin in breast milk.

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