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Methicillin use while Breastfeeding

Medically reviewed by Last updated on Aug 19, 2022.

Drugs containing Methicillin: Staphcillin

Methicillin Levels and Effects while Breastfeeding

Summary of Use during Lactation

Amounts of methicillin ingested by the infant in breastmilk are small and would not be expected to cause any adverse effects. 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. Methicillin is acceptable in nursing mothers.

Drug Levels

Maternal Levels. Intramuscular injections of methicillin 1 gram every 6 hours for 6 to 9 days in 17 women with monolateral mastitis yielded methicillin levels in milk that reached a peak of 0.31 mg/L at 3 hours after the first dose on the first day in the healthy breast, and much lower levels in the breast with mastitis. After the last dose, peak milk levels of 1.53 mg/L occurred 6 hours after the dose. Methicillin milk levels from both breasts were equal.[1]

After a single intramuscular dose of 1 gram of methicillin in 3 women, milk levels ranged from 0.2 to 0.3 mg/L between 1 and 6 hours.[2]

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

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


Kulakov VI, Zak IR, Kulikova NN, et al. Antibiotiki. 1981;26:110–3. [Body pharmacokinetics of methicillin, oxacillin and cephaloridine in puerperal mastitis] [PubMed: 7212690]
Matsuda S. Transfer of antibiotics into maternal milk. Biol Res Pregnancy Perinatol. 1984;5:57–60. [PubMed: 6743732]

Substance Identification

Substance Name


CAS Registry Number


Drug Class

Breast Feeding


Anti-Infective Agents

Antibacterial Agents


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Further information

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