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Drugs and Lactation Database (LactMed) [Internet]. Bethesda (MD): National Library of Medicine (US); 2006-.

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Drugs and Lactation Database (LactMed) [Internet].

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Mifepristone

Last Revision: July 18, 2022.

Estimated reading time: 2 minutes

CASRN: 84371-65-3

image 135014465 in the ncbi pubchem database

Drug Levels and Effects

Summary of Use during Lactation

Limited information indicates that breastfeeding need not be interrupted after a single dose of mifepristone as in a medical abortion, but a dose of 200 mg might be preferable to a 600 mg dose in nursing mothers. Breastfeeding should be avoided during long-term therapy as a cortisol receptor blocker for controlling hyperglycemia. Because of its long half-life, the manufacturer recommends pumping and discarding milk during long-term therapy and for 18 to 21 days after the last dose.

Drug Levels

Maternal Levels. Twelve women (most 6 to 12 months postpartum) who had undergone a medical abortion using mifepristone and misoprostol provided milk samples for up to 5 days after the procedure for measurement of mifepristone. In the 2 women who received a single dose of 200 mg orally, mifepristone was undetectable (<5.6 mcg/L) in breastmilk at all times. Among the 10 women who received a single oral dose of 600 mg, average mifepristone breastmilk levels were 172 mcg/L on day 1 (n = 9) ; 66 mcg/L on day 2 (n = 9); 31 mcg/L on day 3 (n = 10); 24 mcg/L on day 4 (n = 4); and 25 mcg/L on day 5 (n = 3). Breastmilk levels of mifepristone were highest in the samples collected between 6 and 9 hours after drug administration. Samples collected between 9 and 15 hours after the dose had much lower mifepristone levels. The authors estimated that a fully breastfed infant would receive a weight-adjusted dosage of 0.5% of the maternal dosage. They suggested that breastfeeding need not be interrupted after a single dose of mifepristone and that a dose of 200 mg might be preferable to a 600 mg dose in nursing mothers.[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

Based on animal data, some authors suggest that mifepristone used at term might shorten the onset of lactation, increase milk flow and increase the initial growth rate of breastfed infants.[2-4] However, no human data are available.

References

1.
Sääv I, Fiala C, Hämäläinen JM, et al. Medical abortion in lactating women - low levels of mifepristone in breast milk. Acta Obstet Gynecol Scand. 2010;89:618–22. [PubMed: 20367522]
2.
Baird DT. Antigestogens. Br Med Bull. 1993;49:73–87. [PubMed: 8324617]
3.
Permezel M. The antiprogesterone steroid, RU 486 (mifepristone). Aust N Z J Obstet Gynaecol. 1990;30:77–80. [PubMed: 2189395]
4.
Ulmann A, Dubois C. Anti-progesterones in obstetrics, ectopic pregnancies and gynaecological malignancy. Baillieres Clin Obstet Gynaecol. 1988;2:631–8. [PubMed: 3069266]

Substance Identification

Substance Name

Mifepristone

CAS Registry Number

84371-65-3

Drug Class

Breast Feeding

Lactation

Milk, Human

Contraceptives, Oral, Synthetic

Contraceptives, Postcoital, Synthetic

Hormone Antagonists

Luteolytic Agents

Menstruation-Inducing Agents

Abortifacient Agents, Steroidal

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.

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