Last update March 24, 2019


High Risk

Poorly safe. Evaluate carefully. Use safer alternative or interrupt breastfeeding 3 to 7 T ½ (elimination half-lives). Read the Comment.

Fluorouracil is an analogue of uracil that acts as an antimetabolite and is used as a treatment for common malignant neoplasms, particularly colon and breast cancer, administered intravenously every 24 hours or weekly.

It is excreted in breastmilk in undetectable, clinically insignificant amounts (Peccatori 2012) which can be explained by its pharmacokinetics: rapid degradation to non-active metabolites and very low liposolubility (Pistilli 2013).

It is known from pharmacokinetics that after 3 elimination half-lives (T½) 87.5% of the drug is eliminated from the body; after 4 T½ it is 94%, after 5 T½, 96.9%, after 6 T½, 98.4% and after 7 T½, 99%. From 7 T½ the plasma concentrations of the drug in the body are negligible. In general, a period of at least five half-lives can be considered a safe waiting period before breastfeeding again (Anderson 2016).

Taking the longest T½ published as a reference, these 5 T½ would correspond to 1.7 hours. Due to major side effects, it would be advisable to wait 7 T½, which would correspond to 2.5 hours. Meanwhile, express and discard milk from the breast regularly. Some authors recommend waiting 24 hours (89 T½) after the last dose (IV, IM, IP) to restart breastfeeding (Hale 2017 p388).
When it is possible to do so, milk detections in each patient to determine the total elimination of the drug would be the best indicator before resuming breastfeeding between two cycles of chemotherapy.

The administration of 5-Fluorouracil does not reduce milk production (Pistilli 2013, Peccatori 2012).

In intraocular treatments, doses are minimal and there is unlikely to be excretion in breastmilk (Hale 2017 p388).

During breast cancer treatment, breastfeeding must be interrupted due to potentially serious side effects for the infant. Chemotherapy does not affect milk production during or after treatment.
Abrupt weaning can be psychologically traumatic for both the mother and the infant (Pistilli 2013). If the mother wishes, production of milk can be maintained by regular expressing of the breast, resumption of breastfeeding being possible in the periods in which no significant traces of the drug remain in the milk (Anderson 2016) or at the end of the treatment (Pistilli 2013).

Some chemotherapeutic agents with an antibiotic effect can alter the composition of the microbiota (bacterial set or bacterial flora) of breastmilk and the concentration of some of its components (Urbaniak 2014). This possibly occurs temporarily with subsequent recovery, although no harmful effects are assumed or have been reported in breastfed infants.

Women undergoing chemotherapy during pregnancy have lower rates of breastfeeding due to difficulties in breastfeeding (Stopenski 2017), needing more support to achieve it.

Given the strength of the existing evidence on the benefits of breastfeeding for the development of babies and the health of mothers, the risk-benefit of any maternal treatment should be evaluated, including chemotherapy, individually advising each mother who wishes to continue with breastfeeding (Koren 2013).

See below the information of these related products:

  • Capecitabine ( Poorly safe. Evaluate carefully. Use safer alternative or interrupt breastfeeding 3 to 7 T ½ (elimination half-lives). Read the Comment.)
  • Fluorouracil (Topical use) (Possibly safe. Probably compatible. Mild risk possible. Follow up recommended. Read the Comment.)
  • Maternal Cancer ( Poorly safe. Evaluate carefully. Use safer alternative or interrupt breastfeeding 3 to 7 T ½ (elimination half-lives). Read the Comment.)


We do not have alternatives for Fluorouracil.

Suggestions made at e-lactancia are done by APILAM team of health professionals, and are based on updated scientific publications. It is not intended to replace the relationship you have with your doctor but to compound it. The pharmaceutical industry contraindicates breastfeeding, mistakenly and without scientific reasons, in most of the drug data sheets.

Jose Maria Paricio, Founder & President of APILAM/e-Lactancia

Your contribution is essential for this service to continue to exist. We need the generosity of people like you who believe in the benefits of breastfeeding.

Thank you for helping to protect and promote breastfeeding.

José María Paricio, founder of e-lactancia.

Other names

Fluorouracil is also known as

Fluorouracil in other languages or writings:


Fluorouracil belongs to this group or family:


Main tradenames from several countries containing Fluorouracil in its composition:


Variable Value Unit
Oral Bioavail. 50 - 80 %
Molecular weight 130 daltons
Protein Binding 10 (8 - 12) %
VD 15.5 l/Kg
pKa 7.76 -
Tmax 0 ( iv ) hours
0.27 (0.13 - 0.34) hours
M/P ratio 0.0045 -
Theoretical Dose < 0.0098 mg/Kg/d
Relative Dose 0.08 - 0.17 %


  1. Stopenski S, Aslam A, Zhang X, Cardonick E. After Chemotherapy Treatment for Maternal Cancer During Pregnancy, Is Breastfeeding Possible? Breastfeed Med. 2017 Mar;12:91-97. Abstract
  2. Hale TW, Rowe HE. Medications & Mothers' Milk. A Manual of Lactation Pharmacology. Springer Publishing Company. 2017
  3. Anderson PO. Cancer Chemotherapy. Breastfeed Med. 2016 May;11:164-5. Abstract Full text (link to original source) Full text (in our servers)
  4. Urbaniak C, McMillan A, Angelini M, Gloor GB, Sumarah M, Burton JP, Reid G. Effect of chemotherapy on the microbiota and metabolome of human milk, a case report. Microbiome. 2014 Jul 11;2:24. Abstract Full text (link to original source) Full text (in our servers)
  5. Pistilli B, Bellettini G, Giovannetti E, Codacci-Pisanelli G, Azim HA Jr, Benedetti G, Sarno MA, Peccatori FA. Chemotherapy, targeted agents, antiemetics and growth-factors in human milk: how should we counsel cancer patients about breastfeeding? Cancer Treat Rev. 2013 May;39(3):207-11. Abstract
  6. Koren G, Carey N, Gagnon R, Maxwell C, Nulman I, Senikas V; Society of Obstetricians and Gynaecologists of Canada. Cancer chemotherapy and pregnancy. J Obstet Gynaecol Can. 2013 Mar;35(3):263-278. Abstract Full text (link to original source) Full text (in our servers)
  7. Peccatori FA, Giovannetti E, Pistilli B, Bellettini G, Codacci-Pisanelli G, Losekoot N, Curigliano G, Azim HA Jr, Goldhirsch A, Peters GJ. "The only thing I know is that I know nothing": 5-fluorouracil in human milk. Ann Oncol. 2012 Abstract Full text (link to original source) Full text (in our servers)

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