Drug Levels and Effects:

Summary of Use during Lactation:

Most sources consider breastfeeding to be contraindicated during maternal antineoplastic drug therapy. Limited information indicates that a maternal continuous intravenous fluorouracil infusion at a dose of 200 mg/square meter daily produces undetectable levels in milk. If fluorouracil use is undertaken, monitoring of the infant's complete blood count and differential is advisable.Topicalfluorouracil applied away from the breast should pose negligible risk for the breastfed infant; however, it is important to ensure that the infant's skin does not come into direct contact with the areas of skin that have been treated.

Drug Levels:

Maternal Levels.

A mother who was 9 months postpartum was diagnosed with rectal cancer and began treatment with pelvic radiotherapy and a continuous intravenous infusion of fluorouracil 200 mg/square meter daily. Her plasma fluorouracil concentration was constant at about 110 micromoles/L (14.3 mg/L) from weeks 2 to5of therapy. She discontinued nursing her infant and pumped her breasts twice daily and collected 36 breastmilk samples before, during and for 10 days following fluorouracil therapy (exact times not specified). Fluorouracil was undetectable (<0.5micromol/L [<65 mcg/l])="" in="" all="" of="" the="" milk="">

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.

Possible Effects on Lactation:

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


Peccatori FA, Giovannetti E, Pistilli B et al. "The only thing I know is that I know nothing":5-fluorouracil in human milk. Ann Oncol. 2012;23:543-4. PMID:22275286

Substance Identification:

Substance Name:


CAS Registry Number:


Drug Class:

  • Antimetabolites

  • Antimetabolites, Antineoplastic

  • Immunosuppressive Agents

  • Administrative Information:

    LactMed Record Number:


    Last Revision Date:

    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.