Can I take letrozole while pregnant or breastfeeding?

8.1 Pregnancy Risk Summary Based on postmarketing reports, findings from animal studies and the mechanism of action, letrozole can cause fetal harm and is contraindicated for use in pregnant women. In post-marketing reports, use of letrozole during pregnancy resulted in cases of spontaneous abortions and congenital birth defects; however, the data are insufficient to inform a drug-associated risk [see Contraindications (4) , Warnings and Precautions (5.6) , Adverse Reactions (6.2) , and Clinical Pharmacology (12.1) ]. In animal reproduction studies, administration of letrozole to pregnant animals during organogenesis resulted in increased post-implantation pregnancy loss and resorption, fewer live fetuses, and fetal malformation affecting the renal and skeletal systems in rats and rabbits at doses approximately 0.1 times the daily maximum recommended human dose (MRHD) on a mg/m 2 basis (see Data). The background risk of major birth defects and miscarriage for the indicated population is unknown. However, the background risk in the U.S. general population of major birth defects is 2% to 4% and of miscarriage is 15% to 20% of clinically recognized pregnancies.

Prescribing label, section “8.1 Pregnancy” (opening excerpt): Letrozole (oral), Aurobindo Pharma Limited. Read the full section on DailyMed. Quoted verbatim; US labels are written for US prescribers and patients.

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.

“Summary of Use during Lactation”, LactMed record “Letrozole” (LM1344), quoted verbatim. Everything LactMed reports about Letrozole while breastfeeding.

8.2 Lactation Risk Summary It is not known if letrozole is present in human milk. There are no data on the effects of letrozole on the breastfed infant or milk production. Exposure of lactating rats to letrozole was associated with impaired reproductive performance of the male offspring (see Data) . Because of the potential for serious adverse reactions in breastfed infants from letrozole, advise lactating women not to breastfeed while taking letrozole and for at least 3 weeks after the last dose.

Prescribing label, section “8.2 Lactation” (opening excerpt): Letrozole (oral), Aurobindo Pharma Limited. Read the full section on DailyMed. Quoted verbatim; US labels are written for US prescribers and patients.