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 B: Animal reproduction studies have failed to demonstrate a risk to the fetus and there are no adequate and well-controlled studies in pregnant women.

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: B

See references

Use is considered acceptable; caution is recommended.

Excreted into human milk: Yes

Comments:
-The effects in the nursing infant are unknown.
-Limited data indicate that low levels in milk from single maternal doses are not expected to cause harmful effects in nursing infants.
-Some experts recommend an alternative feeding method to avoid possible sensitization of the newborn.

Single or multiple doses of penicillin G (benzylpenicillin), 100,000 units once or every 2 hours for 6 hours, were administered to 10 women. At 1 to 2 hours after dosing, milk levels ranged from unmeasurable to 30 units/L after a single dose and averaged 50 units/L after multiple doses.

A single IM dose of penicillin G was administered to 10 women. Milk levels were about 60 units/L and relatively constant for 6 hours after a 200,000-unit dose in 4 women. At 2 to 4 hours after a 500,000-unit dose in 4 women, milk levels reached 240 units/L. Peak levels of 240 to 360 units/L occurred at 4 hours after a 600,000-unit dose in 2 women.

After 2 IM doses (2 million units/dose) of penicillin G in 15 women, peak and trough milk levels were 120 and 10 units/L, respectively. After 2 IM doses (4 million units/dose) in 5 women, peak and trough milk levels were 220 and 30 units/L, respectively. Peak levels occurred 3 to 6 hours postdose.

After an IM dose of 360 mg (about 550,000 units) of penicillin G in 2 women, milk levels averaged 0.35 mg/L (530 units/L) at 1 hour, 0.2 mg/L (300 units/L) at 2 hours, and 0.1 mg/L (150 units/L) at 4 hours after dosing; at 6 hours postdose, only a trace was detectable.

A Herxheimer's 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.

Disruption of infant's gastrointestinal flora (resulting in diarrhea or thrush) reported occasionally with penicillins; such effects have not been adequately evaluated.

See references