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Cyclophosphamide use while Breastfeeding

Drugs containing Cyclophosphamide: Cytoxan, Cytoxan Lyophilized, Neosar

Medically reviewed by Last updated on Nov 15, 2018.

Cyclophosphamide Levels and Effects while Breastfeeding

Summary of Use during Lactation

Cyclophosphamide appears in milk in potentially toxic amounts; additionally, highly toxic active metabolites could add to the risk to the infant. Neutropenia has been reported in 2 infants whose mothers breastfed them while receiving cyclophosphamide. Chemotherapy may adversely affect the normal microbiome and chemical makeup of breastmilk.[1] Women who receive chemotherapy during pregnancy are more likely to have difficulty nursing their infant. Most sources consider breastfeeding to be contraindicated during maternal cytotoxic antineoplastic drug therapy, especially alkylating agents such as cyclophosphamide.[2]

Drug Levels

Maternal Levels. Unmetabolized cyclophosphamide was qualitatively detected in milk 1, 3, 5 and 6 hours after IV injection of 500 mg of drug in one patient.[3][4] Quantitative determination was not reported.

A mother who had been exclusively breastfeeding for 6 months was diagnosed with multiple sclerosis. In preparation for stem cell transplantation, she received intravenous cyclophosphamide 2.8 grams daily for 4 consecutive days. She was also receiving anti-thymocyte immune globulin, methylprednisolone, mesna, and furosemide. She provided milk samples several times on each of the 4 days for analysis of cyclophosphamide. No metabolites, including active metabolites, were measured. Peak cyclophosphamide milk levels occurred at 4 to 5 hours each day. However, the level of exposure was lower on each successive day, presumably because of autoinduction of the drug's metabolism. Peak level ranged from 40.8 mg/L on day 1 to 13.2 mg/L on day 4; the average level ranged from 15.1 mg/L on day 1 to 3.1 mg/L on day 4; and, the estimated daily infant dosage ranged from 2.3 mg/kg on day 1 to 0.5 mg/kg on day 4. The weight-adjusted percentage of the maternal dosage ranged from 4.8% on day 1 to 0.9% on day 4.[5]

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

Effects in Breastfed Infants

In one 23-day-old infant, neutropenia, thrombocytopenia and a low hemoglobin were possibly caused by cyclophosphamide after 3 days of maternal treatment with cyclophosphamide 6 mg/kg IV daily (total dose 300 mg).[6]

In a 4-month-old, neutropenia was probably caused by cyclophosphamide in a mother 9 days after the last of 6 weekly doses of 800 mg cyclophosphamide intravenously, 2 mg vincristine intravenously and daily doses of 30 mg of prednisolone orally. Neutropenia persisted at least 12 days and was accompanied by a brief episode of diarrhea.[7]

Effects on Lactation and Breastmilk

Telephone follow-up study was conducted on 74 women who received cancer chemotherapy at one center during the second or third trimester of pregnancy to determine if they were successful at breastfeeding postpartum. Only 34% of the women were able to exclusively breastfeed their infants, and 66% of the women reported experiencing breastfeeding difficulties. This was in comparison to a 91% breastfeeding success rate in 22 other mothers diagnosed during pregnancy, but not treated with chemotherapy. Other statistically significant correlations included: 1. mothers with breastfeeding difficulties had an average of 5.5 cycles of chemotherapy compared with 3.8 cycles among mothers who had no difficulties; and 2. mothers with breastfeeding difficulties received their first cycle of chemotherapy on average 3.4 weeks earlier in pregnancy. Of the 56 women who received a cyclophosphamide-containing regimen, 34 had breastfeeding difficulties.[8]


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. 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

3. Duncan JH, Colvin OM, Fenselau C. Mass spectrometric study of the distribution of cyclophosphamide in humans. Toxicol Appl Pharmacol. 1973;24:317-23. PMID: 4741053

4. Wiernik PH, Duncan JH. Cyclophosphamide in human milk. Lancet. 1971;1(7705):912. PMID: 4102054

5. Fierro ME, Datta P, Rewers-Felkins K et al. Cyclophosphamide use in multiple sclerosis: Levels detected in human milk. Breastfeed Med. 2019;14:128-30. PMID: 30589584

6. Durodola JI. Administration of cyclophosphamide during late pregnancy and early lactation: a case report. J Nat Med Assoc. 1979;71:165-6. PMID: 423292

7. Amato D, Niblett JS. Neutropenia from cyclophosphamide in breast milk. Med J Aust. 1977;1:383-4. PMID: 859486

8. Stopenski S, Aslam A, Zhang X et al. After chemotherapy treatment for maternal cancer during pregnancy, is breastfeeding possible? Breastfeed Med. 2017;12:91-7. PMID: 28170295

Cyclophosphamide Identification

Substance Name


CAS Registry Number


Drug Class

Breast Feeding


Antineoplastic Agents

Alkylating Agents

Administrative Information

LactMed Record Number



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