Can you take trastuzumab while breastfeeding?
What LactMed says
The National Library of Medicine’s own summary, quoted in full. We do not write a verdict of our own on this question, and we do not compress theirs into a label.
Trastuzumab milk concentrations were collected in one mother. Concentrations were low, consistent with it being a large protein molecule with a molecular weight of about of 145,531 Da. It is also likely to be partially destroyed in the infant's gastrointestinal tract and absorption by the infant is probably minimal. Until more data become available, trastuzumab should be used with caution during breastfeeding, especially while nursing a newborn or preterm infant. The manufacturer recommends that breastfeeding be discontinued during trastuzumab therapy and for 7 months after the last dose.
Quoted from Trastuzumab — Drugs and Lactation Database (LactMed®), National Institute of Child Health and Human Development, revised June 15, 2026.
How much trastuzumab gets into breastmilk
Maternal Levels. A woman was diagnosed with breast cancer in pregnancy and received five cycles of 75 mg docetaxel during pregnancy. As soon as clinically feasible postpartum, she was given trastuzumab 600 mg intravenously in the first cycle. Fifteen milk samples were collected over 17 days after the first dose except for days 6, 8, and 14 because no milk was produced on those days. Milk trastuzumab concentrations ranged between 12.7 and 977 mcg/L, with the highest concentration found 10 days after the dose. The authors calculated relative infant dosage in a nonstandard way that did not take low oral bioavailability into account, thereby overstating infant exposure, so it is not reported here.
Infant Levels. Relevant published information was not found as of the revision date.
What has been seen in breastfed infants
Relevant published information was not found as of the revision date.
Effects on milk supply
Relevant published information was not found as of the revision date.
Frequently asked questions
Can you take trastuzumab while breastfeeding?
Trastuzumab milk concentrations were collected in one mother. The full record is quoted on this page, and the decision is one to make with the person who prescribed it — LactMed itself states it is not a substitute for professional judgement.
Does trastuzumab pass into breastmilk?
LactMed's measured drug levels for trastuzumab are quoted in full on this page, under "How much gets into breastmilk".
Do I need to pump and dump after taking trastuzumab?
LactMed does not frame its records that way — it reports measured drug levels in milk and what has been observed in breastfed infants, which is what this page quotes. "Pump and dump" advice for a specific drug and dose should come from your clinician or a pharmacist, not from a general rule.
More on trastuzumab
LactMed states that the information it presents is not a substitute for professional judgement, and that you should consult your healthcare provider for breastfeeding advice related to your particular situation. Nothing on this page is medical advice.