Mifepristone. A review of its pharmacodynamic and pharmacokinetic properties, and therapeutic potential.

Mifepristone is a potent oral antiprogestogen which acts at the level of the receptor, having a high affinity for the progesterone receptor. Most of the clinical trials have studied its efficacy in the termination of early pregnancy when used in conjunction with a low dosage of a prostaglandin analogue. In these studies, mifepristone 100 to 600mg administered as a single dose or over 3 or 4 days, 36 to 48 hours before a prostaglandin analogue given vaginally, intramuscularly or orally, induced complete abortion in about 95% of women. Used alone, mifepristone is an effective cervical priming agent prior to termination of first trimester pregnancy by vacuum aspiration, and facilitates termination of second trimester pregnancy by prostaglandin by reducing the interval between the start of prostaglandin treatment and termination, the cumulative prostaglandin dosage, and the adverse effects associated with these drugs. Mifepristone can also be used to induce labour in cases of intrauterine fetal death. Mifepristone has been shown to be an effective postcoital contraceptive with a likely emergency role, since its repeated use modifies the menstrual cycle. Pilot studies have been performed in unresectable meningioma and metastatic breast cancer, and in Cushing's syndrome. Mifepristone is generally well tolerated, and thus is an effective, appropriate, medical alternative to surgical termination of early pregnancy. It has as yet unexplored potential as a postcoital contraceptive and in oncology.