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Hydroxyurea use while Breastfeeding

Drugs containing Hydroxyurea: Hydrea, Droxia, Siklos, Mylocel

Medically reviewed on Nov 30, 2017

Hydroxyurea Levels and Effects while Breastfeeding

Summary of Use during Lactation

Most sources consider breastfeeding to be contraindicated during maternal antineoplastic drug therapy, although the evidence for this recommendation is very weak.[1][2] Although only minimal data are available to determine an appropriate period to withhold breastfeeding, the drug's terminal half-live of 4.5 hours with normal kidney function suggests that withholding breastfeeding for at least 24 hours may be sufficient for patients receiving intermittent therapy. This period may be longer in patients with impaired kidney function. Chemotherapy may adversely affect the normal microbiome and chemical makeup of breastmilk.[3]

Drug Levels

Maternal Levels. A mother was taking 500 mg of hydroxyurea orally three times a day. Milk samples taken 2 hours after the last dose of each day on 3 days averaged 6.1 mg/L (range 3.8 to 8.4 mg/L). Using these data, the infant in this case would have received less than 4% of maternal weight-adjusted dosage.[4]

Using a more modern assay, investigators measured hydroxyurea in a mother who was taking an oral dose of 1 gram once daily. Nine milk samples were taken over a 3-day period. Trough levels ranged from 0.51 to 1.23 mg/L and the highest level was 19.24 mg/L ay 3 hours after the dose on one day. All other measurements fell between these values.[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.


1. Pistilli B, Bellettini G, Giovannetti E et al. Chemotherapy, targeted agents, antiemetics and growth-factors in human milk: How should we counsel cancer patients about breastfeeding? Cancer Treat Rev. 2013;39:207-11. PMID: 23199900

2. National Institutes of Health. National Heart Lung and Blood Institute. Evidence-based management of sickle cell disease. Expert panel report. 2014.

3. Urbaniak C, McMillan A, Angelini M et al. Effect of chemotherapy on the microbiota and metabolome of human milk, a case report. Microbiome. 2014;2:24. PMID: 25061513

4. Sylvester RK, Lobell M, Teresi ME et al. Excretion of hydroxyurea into milk. Cancer. 1987;60:2177-8. PMID: 3481556

5. Marahatta A, Ware RE. Hydroxyurea: Analytical techniques and quantitative analysis. Blood Cells Mol Dis. 2017;67:135-42. PMID: 28847416

Hydroxyurea Identification

Substance Name


CAS Registry Number


Drug Class

Antineoplastic Agents

Administrative Information

LactMed Record Number



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Further information

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