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Antiprogestogen
Antiprogestogen
Drug class
	Mifepristone, an antiprogestogen that is used to induce medical abortions.
Class identifiers
Synonyms	Antiprogestins; Progesterone antagonists; Progesterone blockers
Use	Medical abortion, emergency contraception, uterine fibroids
ATC code	G03XB
Biological target	Progesterone receptor
Chemical class	Steroidal
Legal status
	In Wikidata

Antiprogestogens or antiprogestins, also known as progesterone antagonists or progesterone blockers, are a class of drugs which prevent progestogens like progesterone from mediating their biological effects in the body. These drugs competitively inhibit progestin at progesterone receptors, acting by blocking the progesterone receptor (PR) and/or inhibiting or suppressing progestogen production. Antiprogestogens are one of three types of sex hormone antagonists, alongside antiestrogens and antiandrogens.^[1]

Clinical applications

Antiprogestogens are used as abortifacients, emergency contraceptives, and in the treatment of uterine fibroids. They are also being studied in the treatment of breast cancer. Examples include the progesterone receptor weak partial agonist mifepristone, the selective progesterone receptor modulator (SPRM) ulipristal acetate, and the silent antagonist aglepristone.^[2]^[3] In medical abortion, mifepristone is combined with a prostaglandin (e.g., gemeprost), while ulipristal is used for emergency contraception.^[4]

Development and approval

Several hundred antiprogestogens have been developed, but only three—mifepristone, lilopristone, and onapristone—have been administered to humans. Of these, only mifepristone has been approved and introduced for clinical use.^[5]

Role and mechanism of action

Progestins, including progesterone, are vital for preparing the uterus for the implantation of a fertilized egg during the luteal phase of the menstrual cycle. If fertilization, implantation, and other events necessary for pregnancy occur, increased progestin (i.e., progesterone) levels are essential in maintaining the pregnancy. Blocking the effects of progestins like progesterone is associated with anti-gestational effects, resulting in the interruption of pregnancy maintenance.^[4]

References

^ Nath JL (2006). Using Medical Terminology: A Practical Approach. Lippincott Williams & Wilkins. pp. 977–. ISBN 978-0-7817-4868-1.
^ Spitz IM (October 2006). "Progesterone receptor antagonists". Current Opinion in Investigational Drugs. 7 (10): 882–890. PMID 17086932.
^ Tang OS, Ho PC (December 2006). "Clinical applications of mifepristone". Gynecological Endocrinology. 22 (12): 655–659. doi:10.1080/09513590601005946. PMID 17162706. S2CID 23295715.
^ ^a ^b Le T, Bhushan V, Qiu C, Chalise A, Kaparaliotis P (2023). First aid for the USMLE step 1. McGraw Hill. ISBN 978-1-264-94662-4.
^ Nielsen S, Granberg S (17 October 2006). "The expectant management of miscarriage". In Bourne TH, Condous G (eds.). Handbook of Early Pregnancy Care. CRC Press. pp. 37–50 (41). ISBN 978-0-203-01621-3.