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Drugs and Lactation Database (LactMed®) [Internet]. Bethesda (MD): National Institute of Child Health and Human Development; 2006-.

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Drugs and Lactation Database (LactMed®) [Internet].

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Last Revision: October 31, 2018.

Estimated reading time: 3 minutes

CASRN: 69-53-4

Chemical structure

Drug Levels and Effects

Summary of Use during Lactation

Substantial information indicates that ampicillin produces 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 have been reported with penicillins, but these effects have not been adequately evaluated. Ampicillin is acceptable in nursing mothers.

Drug Levels

Maternal Levels. After an ampicillin oral dose of 500 mg every 6 hours for 3 days, milk levels fluctuated little and ranged from 0.575 to 1 mg/L (mean 0.8 mg/L) at various times in one mother and 0.014 mg/L to 0.0675 mg/L (average 0.03 mg/L) in another.[1]

In 10 mothers given ampicillin 1.5 or 2 grams daily by mouth for 3 doses had milk levels ranging from 0.03 to 0.2 mg/L. Another mother receiving 3 grams daily by mouth had milk levels of 0.08 to 0.3 mg/L. In 3 mothers who received 2 grams daily intramuscularly, milk levels ranged from 0.3 to 0.9 mg/L and in 3 mothers who received 4 grams daily intramuscularly had milk levels of 0.4 to 0.9 mg/L. In all cases, peak milk levels occurred 3 hours after the dose. The breastfed infant was estimated to receive from 0.08 to 0.2 mg daily of ampicillin with these doses.[2]

A study in postpartum women with endometritis who received ampicillin 1 or 2 grams infused intravenously over 20 minutes found the average milk levels of ampicillin to be 1.7 mg/L with the highest level observed 3 mg/L.[3]

In 15 women receiving ampicillin 500 mg 4 times daily by intramuscular injection, average milk ampicillin levels were as follows: 0.11 mg/L at 30 minutes after the injection; 0.21 mg/L at 1 hour, 0.17 at 2 hours, 0.27 mg/L at 4 hours and 0.26 mg/L at 6 hours after the injection.[4]

In 13 women with mastitis who received 1 gram of ampicillin orally 4 times daily, the average milk concentrations ranged from 0.6 to 1.05 mg/L.[5]

In 15 women given a single 2 grams dose of ampicillin intravenously, milk levels averaged 1.1 mg/L 2 hours after the dose.[6]

Infant Levels. Thirteen women with mastitis received 1 gram of ampicillin orally 4 times daily. Ampicillin was detectable in the urine in only 2 of 8 of the breastfed infants in whom it was measured.[5]

Effects in Breastfed Infants

An uncontrolled observation of the breastfed infants of mothers taking ampicillin noted a seeming increase in cases of diarrhea and candidiasis that was attributed to ampicillin in breastmilk.[7]

In a prospective follow-up study, 5 nursing mothers reported taking ampicillin (dosage unspecified). One mother reported diarrhea in her infant. No rashes or candidiasis were reported among the exposed infants.[8]

A small, controlled, prospective study had mothers monitor their infants for signs of adverse effects (furring of the tongue, feeding difficulties, changes in stool frequency and consistency, diaper rash, and skin rash). Weight change and the development of jaundice were also recorded. No statistical differences in these parameters were found between the infants of the control mothers and those of mothers taking ampicillin.[9]

Effects on Lactation and Breastmilk

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


Lohmeyer H, Halfpap E. [Pharmacokinetic studies and clinical experiences with ampicillin during treatment of infections of the urogenital tract of the female]. Z Geburtshilfe Gynakol. 1965;164:184-202. [PubMed: 5887161]
Pons G, Rey E. [Passage of antibiotics in breast milk]. Med Mal Infect. 1994;24 (Special Issue 1):1088-106. DOI: 10.1016/S0399-077X(05)80220-3. [CrossRef]
Foulds G, Miller RD, Stankewich JP et al. The pharmacokinetics of subactam and ampicillin in postpartum women. In: Spitzy KH, Karrer K, eds. Proc 13th Int Congress Chemother. 1983;1:23-17-23/22.
Amiraslanova LA, Emel'ianova AI, Fursova SA, Rukhadze TG. [Various characteristics of the pharmacokinetics of ampicillin, kanamycin and cefuroxime in puerperants with endometritis]. Akush Ginekol (Mosk). 1985;Oct; (10):14-7. [PubMed: 2934996]
Peiker G, Schroder S. [The concentration of oxacillin and ampicillin (Penstabil) in mother's milk in puerperal mastitis.] Untersuchungen zur konzentration von oxacillin und ampicillin (Penstabil) in serum und muttermilch bei der mastitis puerperalis. Pharmazie. 1986;41(11):793-5. [PubMed: 3562514]
Zhang Y, Zhang Q, Xu Z. [Tissue and body fluid distribution of antibacterial agents in pregnant and lactating women]. Zhonghua Fu Chan Ke Za Zhi. 1997;32(5):288-92. [PubMed: 9596854]
Williams M. Excretion of drugs in milk. Pharm J. 1976;217:219. Letter.
Ito S, Blajchman A, Stephenson M et al. Prospective follow-up of adverse reactions in breast-fed infants exposed to maternal medication. Am J Obstet Gynecol. 1993;168:1393-9. [PubMed: 8498418]
Campbell AC, McElnay JC, Passmore CM. The excretion of ampicillin in breast milk and its effect on the suckling infant. Br J Clin Pharmacol. 1991;31:230p. Abstract. PMC: PMC1368401.

Substance Identification

Substance Name


CAS Registry Number


Drug Class

  • Breast Feeding
  • Anti-Infective Agents
  • Antibacterial Agents
  • Penicillins

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.

Copyright Notice

Attribution Statement: LactMed is a registered trademark of the U.S. Department of Health and Human Services.

Bookshelf ID: NBK500994PMID: 30000053


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