Penicillin G

This sheet is about exposure to penicillin G in pregnancy and while breastfeeding. This information is based on available published literature. It should not take the place of medical care and advice from your healthcare provider.

What is penicillin G?

Penicillin G is an antibiotic drug that belongs to a class of antibiotic medications called penicillins. It works by killing bacteria that cause infections and has been used to treat Staphylococcus aureus (Staph) and syphilis. Penicillin G is given intravenously, sometimes called “I.V.”. This involves injecting the medication into a vein.

Sometimes when people find out they are pregnant, they think about changing how they take their medication, or stopping their medication altogether. However, it is important to talk with your healthcare providers before making any changes to how you take your medication. Your healthcare providers can talk with you about the benefits of treating your condition and the risks of untreated illness during pregnancy.

It is important to treat infections in pregnancy. Some infections, such as Staph or syphilis, can increase the chance of pregnancy-related problems or infections in a newborn baby if not properly treated during pregnancy. Syphilis can also be passed to a fetus during any trimester of pregnancy, which can cause health problems in the newborn. MotherToBaby has fact sheets on Staph here: https://mothertobaby.org/fact-sheets/staphylococcus-aureus-pregnancy/ and syphilis here: https://mothertobaby.org/fact-sheets/syphilis/.

I take penicillin G. Can it make it harder for me to get pregnant?

Studies have not been done to see if penicillin can make it harder to get pregnant.

Does taking penicillin G increase the chance of miscarriage?

Miscarriage is common and can occur in any pregnancy for many different reasons. Taking penicillin G in pregnancy is not expected to increase the chance of miscarriage.

Does taking penicillin G increase the chance of birth defects?

Every pregnancy starts out with a 3-5% chance of having a birth defect. This is called the background risk. Multiple studies have looked at the use of penicillin G during pregnancy and have not reported an increased chance of birth defects.

Does taking penicillin G in pregnancy increase the chance of other pregnancy-related problems?

Penicillin G is not expected to cause other pregnancy-related problems, such as preterm delivery (birth before week 37) or low birth weight (weighing less than 5 pounds, 8 ounces [2500 grams] at birth).

Some people are allergic to penicillins. In very rare cases, penicillin G can cause anaphylaxis (severe allergic reaction where the body goes into shock). Anaphylaxis can cause trouble breathing, low blood pressure, dizziness or fainting, and nausea. Severe or uncontrolled anaphylaxis can affect blood flow to the fetus, which could affect the growth and development of the fetus. If you think you are allergic to penicillin, talk with your healthcare provider about this and the best way to treat your condition.

Does taking penicillin G in pregnancy affect future behavior or learning for the child?

Information from limited studies does not suggest that taking penicillin G during pregnancy can increase the chance of behavior or learning issues for the child.

Breastfeeding while taking penicillin G:

Limited information suggests that the amount of penicillin G that gets into breast milk is small. Taking penicillin G is not expected to cause side effects in most infants. Babies who are exposed to penicillins through breast milk might have diarrhea or develop thrush (fungal infection in the mouth). If you suspect the baby has any symptoms (such as diarrhea, white spots in the mouth, or mouth pain), contact the child’s healthcare provider. Be sure to talk to your healthcare provider about all your breastfeeding questions.

If a male takes penicillin G, could it affect fertility or increase the chance of birth defects?

If you are taking penicillin G for an infection that can be transmitted to others by sexual contact (such as syphilis), it is important to treat your infection for your own health and for your partner’s health. Passing infections on to a partner who is pregnant might increase risks to a pregnancy. Your healthcare provider can talk with you about what steps can be taken to help prevent sexual transmission of infections to your partner.

Studies have not been done to see if penicillin G could affect male fertility (ability to get partner pregnant) or increase the chance of birth defects above the background risk. In general, exposures that fathers or sperm donors have are unlikely to increase risks to a pregnancy. For more information, please see the MotherToBaby fact sheet Paternal Exposures at https://mothertobaby.org/fact-sheets/paternal-exposures-pregnancy/.

Selected References:

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• Crider KS, et al. 2009. Antibacterial medication use during pregnancy and risk of birth defects: National Birth Defects Prevention Study. Arch Pediatr Adolesc Med. 163(11):978-985. [PubMed: 19884587]
• Czeizel AE, et al. 1999. A population-based case-control teratological study of three parenteral penicillins G. Congenital Anomalies 39:117-126.
• Dencker BB, et al. 2002. Birth outcome of 1886 pregnancies after exposure to phenoxymethylpenicillin in utero. Clin Microbiol Infect 8:196-201. [PubMed: 12047410]
• Gallager, JS. 1988. Anaphylaxis in pregnancy. Obstet Gynecol 71:491-493. [PubMed: 3347441]
• Greene H, et al. 1946. Excretion of penicillin in human milk following parturition. Am J Obstet Gynecol 51:732-733. [PubMed: 21025164]
• Heinonen OP, et al. 1977. Birth Defects and Drugs in Pregnancy. Publishing Sciences Group: 299-313, 435.
• Jepsen P, et al. 2003. A population-based study of maternal use of amoxicillin and pregnancy outcome in Denmark. Br J Clin Pharmacol 55(2):216-221. [PMC free article: PMC1894737] [PubMed: 12580995]
• Kosim H. 1959. Intrauterine fetal death as a result of anaphylactic reaction to penicillin in a pregnant woman. Dapim Refuiim 18:136-137.
• Meeraus WH, et al. 2015. Association between antibiotic prescribing in pregnancy and cerebral palsy or epilepsy in children born at term: a cohort study using the health improvement network. PLoS One 10(3): e0122034. [PMC free article: PMC4373729] [PubMed: 25807115]
• Nahum GG, et al. 2006. Antibiotic use in pregnancy and lactation: what is and is not known about teratogenic and toxic risks. Obstet Gynecol 107(5):1120-38. [PubMed: 16648419]
• Njotto LL, et al. 2023. Maternal and early-life exposure to antibiotics and the risk of autism and attention-deficit hyperactivity disorder in childhood: a Swedish population-based cohort study. Drug Saf. 46(5):467-478. [PMC free article: PMC10164008] [PubMed: 37087706]
• Ortqvist AK, et al. 2014. Antibiotics in fetal and early life and subsequent childhood asthma: nationwide population based study with sibling analysis. BMJ. 349:g6979. [PMC free article: PMC4247260] [PubMed: 25432937]
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• Simons & Schatz. 2012. Anaphylaxis during pregnancy. J Allergy Clin Immunol 130(3): 597-606. [PubMed: 22871389]