Is Sirolimus safe while breastfeeding?
Here is what LactMed, the Drugs and Lactation Database published by the U.S. National Institute of Child Health and Human Development (NICHD), reports about Sirolimus. The text below is quoted from that source — it is not our own verdict.
Summary of use during breastfeeding
Information from one mother indicates that the amount of sirolimus in milk is very low. Additionally, the oral bioavailability of the drug is poor, so systemic exposure in the infant is likely very low. A few infants have reportedly been breastfed during maternal sirolimus therapy. Until more data become available, sirolimus should be used with caution during breastfeeding, especially while nursing a newborn or preterm infant.
Sirolimus is undetectable in the bloodstream after application to the skin, so use of topical sirolimus is unlikely to affect a nursing infant. Avoid application to the nipple area and ensure that the infant’s skin does not come into direct contact with the areas of skin that have been treated.
Effects on the breastfed infant
One infant was reported breastfed (extent not stated) during maternal therapy with sirolimus, tacrolimus and prednisone in unspecified dosages following a kidney-pancreas transplant. The authors who followed the mother knew of no serious side effects in the infant.[3]
A review of the Transplant Pregnancy Registry International database from 1999 to 2024 found that 4 mothers with transplants had breastfed their infants for at least 4 weeks while taking sirolimus.[4]
Seven women with breastfed their infants (extent not stated) while using sirolimus for treatment of lymphangioleiomyomatosis. At a median age of 3.5 years (range 1 to 6.5 years) no adverse health outcomes had been reported.[2]
Effects on milk supply
Relevant published information was not found as of the revision date.
Levels in milk
Maternal Levels. A woman taking sirolimus for tuberous sclerosis in a dose of 4 mg daily donated a total of 18 milk samples on days 10, 11 and 15 postpartum, although she was not breastfeeding her infant. Milk concentrations ranged from 173 to 492 ng/L, with the highest value 1 hour after the dose.[1] Using the highest level measured, the worst-case RID value would be 0.1%.
Infant Levels. One breastfed infant whose mother was taking sirolimus for lymphangioleiomyomatosis in an unspecified dosage had an undetectable amount of blood sirolimus.[2]
Alternatives LactMed lists
Source: Drugs and Lactation Database (LactMed), National Institute of Child Health and Human Development (NICHD), via NCBI Bookshelf, record “Sirolimus” (LM740). LactMed on NCBI Bookshelf. LactMed is a registered trademark of the U.S. Department of Health and Human Services.
Educational summary of an authoritative source — not medical advice. Never start, stop, or change a medicine while breastfeeding without confirming with your doctor.