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