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Drugs and Lactation Database (LactMed) [Internet]. Bethesda (MD): National Library of Medicine (US); 2006-.

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Drugs and Lactation Database (LactMed) [Internet].

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Last Revision: December 3, 2018.

Estimated reading time: 1 minute

CASRN: 5250-39-5

Chemical structure

Drug Levels and Effects

Summary of Use during Lactation

Floxacillin (flucloxacillin) is not approved for marketing in the United States by the U.S. Food and Drug Administration. It is acceptable to use during breastfeeding and is frequently used abroad to treat mastitis in nursing mothers.[1][2][3] Limited information indicates that floxacillin levels in milk are low and 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. Floxacillin is acceptable in nursing mothers.

Drug Levels

Maternal Levels. One report states that the manufacturer supplied information on floxacillin excretion into breastmilk. After a 250 mg oral dose, a milk level of 0.1 mg/L was measured. Further details are lacking.[4] This value is consistent with that of other penicillins.

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

Effects in Breastfed Infants

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

Effects on Lactation and Breastmilk

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

Alternate Drugs to Consider

(Mastitis) Cephalexin, Dicloxacillin; (Methicillin-resistant Staph. aureus) Doxycycline, Linezolid, Minocycline, Trimethoprim-Sulfamethoxazole, Vancomycin


Scott JA, Robertson M, Fitzpatrick J et al. Occurrence of lactational mastitis and medical management: a prospective cohort study in Glasgow. Int Breastfeed J. 2008;3:21. [PMC free article: PMC2542350] [PubMed: 18721487]
Dixon JM, Khan LR. Treatment of breast infection. BMJ. 2011;342:484-9. [PubMed: 21317199]
Amir LH. ABM clinical protocol #4: Mastitis, revised March 2014. Breastfeed Med. 2014;9:239-43. [PMC free article: PMC4048576] [PubMed: 24911394]
Griffiths AD, Bull FE. Sweat testing for cystic fibrosis. Arch Dis Child. 1978;53:918. Letter. [PMC free article: PMC1545257] [PubMed: 727820]

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.


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