Is Methylnaltrexone 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 Methylnaltrexone. The text below is quoted from that source — it is not our own verdict.
Summary of use during breastfeeding
Methylnaltrexone is not marketed in the United States, but is available in other countries. No information is available on the use of methylnaltrexone during breastfeeding. The manufacturer recommends avoiding breastfeeding in mothers taking methylnaltrexone. Based on pharmacokinetic data, the oral absorption of methylnaltrexone appears to be very low. Observe breastfed infants who have been exposed to opioids during pregnancy or postpartum for signs of opioid withdrawal, especially diarrhea.
Effects on the breastfed infant
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.
Levels in milk
Based on the serum AUC values of oral and subcutaneous methylnaltrexone in the product labeling, it appears that methylnaltrexone has an oral bioavailability of <5%.
Maternal Levels. Relevant published information was not found as of the revision date.
Infant Levels. Relevant published information was not found as of the revision date.
Alternatives LactMed lists
“No published information” means the studies do not exist yet — not that Methylnaltrexone is known to be harmful, and not that it is known to be safe. Your prescriber or pharmacist can weigh your baby's age and whether a better-studied alternative would do the same job. Worth asking before stopping a medicine you need.
Source: Drugs and Lactation Database (LactMed), National Institute of Child Health and Human Development (NICHD), via NCBI Bookshelf, record “Methylnaltrexone” (methylnaltrexone). 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.