mifepristone

Last edited 01/2023 and last reviewed 01/2023

This is a semisynthetic steroid which is used in combination with the prostaglandin gemeprost as an abortifacient.

Mifepristone is a 19-norsteroid, similar in structure to the progestogen norethisterone, but with a substitution of a dimethylaminophenyl group in the 11 beta position. It has a high affinity for the progesterone receptor and thus inhibits the action of endogenous progesterone, which is essential for the maintenance of pregnancy.

If given alone, mifepristone induces abortion in 60-80% of women, depending on the duration of the pregnancy. If used in combination with prostaglandins, then complete abortion occurs in about 95% of women.

Emergency contraception:

• a systematic review concenring emergency contraception concluded that mifepristone middle dose (25-50 mg) was superior to other hormonal regimens (1)

Study evidence shows (2):

• although rare, short-term adverse events are more likely after mifepristone-misoprostol induced abortion (IA) than procedural IA, especially for less serious adverse outcomes

Reference:

• 1. Cheng L et al.Interventions for emergency contraception. Cochrane Database Syst Rev. 2008 Apr 16;(2):CD001324.
• 2. Lui N et al. Short-Term Adverse Outcomes After Mifepristone-Misoprostol Versus Procedural Induced Abortion. Annals of Internal Medicine (3/1/2023)