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Drugs and Lactation Database (LactMed®) [Internet]. Bethesda (MD): National Institute of Child Health and Human Development; 2006-.

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Drugs and Lactation Database (LactMed®) [Internet].

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Letrozole

Last Revision: January 15, 2025.

Estimated reading time: 1 minute

CASRN: 112809-51-5

image 135028595 in the ncbi pubchem database

Drug Levels and Effects

Summary of Use during Lactation

A minimal amount of information on letrozole excretion into milk indicates that the amounts might be of concern. Because of harm reported in animal studies, the manufacturer recommends that breastfeeding be discontinued during letrozole therapy and for 3 weeks after the last dose.

Drug Levels

Maternal Levels. An abstract reported that a relative infant dose of 10.2% was found in nursing mother(s) taking letrozole, who provided 8 milk samples over 24 hours, but other details were not supplied.[1]

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.

References

1.
Monfort A, Jutras M, Martin B, et al. New data on the transfer of untested medication into breast milk. Birth Defects Res 2021;113:831.

Substance Identification

Substance Name

Letrozole

CAS Registry Number

112809-51-5

Drug Class

Breast Feeding

Lactation

Milk, Human

Antineoplastic Agents

Aromatase Inhibitors

Disclaimer: Information presented in this database is not meant as a substitute for professional judgment. You should consult your healthcare provider for breastfeeding advice related to your particular situation. The U.S. government does not warrant or assume any liability or responsibility for the accuracy or completeness of the information on this Site.

Copyright Notice

Attribution Statement: LactMed is a registered trademark of the U.S. Department of Health and Human Services.

Bookshelf ID: NBK500937PMID: 29999996

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