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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: January 18, 2021.

Estimated reading time: 1 minute

CASRN: 3116-76-5

image 134981835 in the ncbi pubchem database

Drug Levels and Effects

Summary of Use during Lactation

Limited information indicates that dicloxacillin levels in milk are very low and are not expected to cause adverse effects in breastfed infants. It is frequently used to treat mastitis in nursing mothers.[1-3] 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. Dicloxacillin is acceptable in nursing mothers.

Drug Levels

Maternal Levels. After a single oral dose of 250 mg of dicloxacillin in 2 women, milk samples were assayed using a bioassay. Milk levels ranged from 200 to 300 mcg/L between 2 and 4 hours after the dose. The drug was undetectable (lower limit of assay not stated) in milk at 1 and 6 hours after the dose.[4]

Three nursing mothers with mastitis were prescribed dicloxacillin 500 mg every 6 hours. They collected milk samples at 0, 1, 2, 3, 4, 5, and 6 hours after a dose on or after the fourth day of therapy by pumping both breasts and combining the resultant milk. Measurement with liquid chromatography mass spectrometry found that the average peak milk concentration was 67.6 mcg/L at 4 hours after the dose and the average concentration was 57.7 mcg/L. These values resulted in an average infant dosage of 8 mcg/kg daily, which is 0.03% of the maternal weight-adjusted dosage.[5]

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


Berth WL, Schauberger CW, Alvarado MA, et al. Telephone-based management of lactation mastitis. J Reprod Med. 2009;54:291–4. [PubMed: 19517693]
Amir LH. ABM clinical protocol #4: Mastitis, revised March 2014. Breastfeed Med. 2014;9:239–43. [PMC free article: PMC4048576] [PubMed: 24911394]
Berens PD. Breast pain: Engorgement, nipple pain, and mastitis. Clin Obstet Gynecol. 2015;58:902–14. [PubMed: 26512442]
Matsuda S. Transfer of antibiotics into maternal milk. Biol Res Pregnancy Perinatol. 1984;5:57–60. [PubMed: 6743732]
Muysson M, Datta P, Rewers-Felkins K, et al. Transfer of dicloxacillin into human milk. Breastfeed Med. 2020;15:715–7. [PubMed: 32678981]

Substance Identification

Substance Name


CAS Registry Number


Drug Class

Breast Feeding


Anti-Infective Agents

Antibacterial Agents


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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