Mifepristone (CAS: 84371-65-3)

Mifepristone is sold outside theUnited Statesby Exelgyn Laboratories as Mifegyne, made inFrance, and is approved for:

1.    Medical termination of intrauterine pregnancies of up to 49 days gestation (up to 63 days gestation inBritainandSweden)

2.    Softening and dilatation of the cervix prior to mechanical cervical dilatation for pregnancy termination

3.    Use in combination with gemeprost for termination of pregnancies between 13 and 24 weeks gestation

4.    Labor induction in fetal death in utero.

Mifepristone is sold in theUnited Statesby Danco Laboratories as Mifeprex, made inChina, and is U.S. Food and

Drug Administration-approved to terminate intrauterine pregnancies of up to 49 days gestation. Under the

FDA-approved regimen, a 600 mg dose is administered by a clinician following a counseling session. Two days later,

a clinician administers 400 µg of another medicine, misoprostol, to induce contractions. In European studies, this

method terminated 96 to 99% of pregnancies of up to 49 days gestation, but in one large multicenter trial in the

United States conducted from September 1994 to September 1995, the efficacy was lower (92%), which the authors

of the study suggested may have been due to lack of experience with this method in the United States and/or the

design of their study. In Europe andChina, an observation period of several hours is required after administration

of misoprostol. If expulsion of fetal tissue does not occur during the observation period, surgical abortion is offered.

There is no required observation period in theUnited States, but it is strongly recommended.

Mifepristone can also be used in smaller doses as an emergency contraceptive; if taken after sex but before ovulation,

it can prevent ovulation and so prevent pregnancy. In this role, a 10 mg dose is not as effective as the 600 mg dose,

but has fewer side-effects. Mifeprex and Mifegyne are only available in 200 mg tablets.

A review of studies in humans found that the contraceptive effects of the 10 mg dose were probably due mainly to its

effects on ovulation, and not inhibition of implantation, but “the knowledge of the mechanism of action remains

incomplete”. Treatment with 200 mg of mifepristone changes steroid receptor expression in the fallopian tube,

inhibits endometrial development, and effectively prevents implantation.

Other uses

Mifepristone is approved for use in theUnited Statesand the EU for the treatment of Cushing’s Syndrome via a

patented preparation manufactured by Corcept Therapeutics.

Other medical applications of mifepristone that have been studied in clinical trials include regular long-term use

as an oral contraceptive, and treatment of HIV infection, uterine fibroids,endometriosis, major depression with

psychotic features, post-traumatic stress disorder, bipolar depression and disorders causing cognitive dysfunction,

post-traumatic stress disorder, chronic multisymptom illness, glaucoma, meningiomas, breast cancer, ovarian

cancer, and prostate cancer.