Fluorouracil

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 (Unsafe. Moderate/severe adverse effects. Compatible under certain circumstances. Follow-up recommended. Use safer alternative or discontinue breastfeeding from 5 to 7 T ½ . Read Commentary.)
• Fluorouracil (Topical use) (Fairly safe. Mild or unlikely adverse effects. Compatible under certain circumstances. Follow-up recommended. Read Commentary.)
• Maternal Cancer (Unsafe. Moderate/severe adverse effects. Compatible under certain circumstances. Follow-up recommended. Use safer alternative or discontinue breastfeeding from 5 to 7 T ½ . Read Commentary.)