[Mifepristone--a controversial drug with great potential]

BACKGROUND

Antiprogestins, agents that inhibit the action of progesterone, are among the most controversial and yet the more interesting therapeutic compounds developed over the past 20 years.

MATERIAL AND METHODS

We present a review of the literature identified through limited searches on Medline, Cochrane and the Internet, with a discussion of the biological, clinical, political and ethical aspects of this important drug.

RESULTS

The first effective antiprogestin in clinical use was mifepristone (also known as RU 486). This agent provides the most effective and safest means of medical abortion. It may also be used as a contraceptive and delivery-inducing agent and in the treatment of spontaneous abortion, ectopic pregnancies, leiomyoma, endometriosis, intrauterine fetal death, Cushing's syndrome and progesterone-dependent malignancies.

INTERPRETATION

The introduction of mifepristone as an abortion-inducing agent has created intense political, ethical and moral controversies which have delayed clinical investigations and evaluations for potential expanded use.

History and perspectives of antiprogestins from the chemist's point of view

The discovery of RU486 and its potent activity as an antiglucocorticoid and antiprogestin brought the long story on steroid hormones and antihormones to its logical conclusion. Even though scattered improvements are still possible, the armamentarium of the steroid endocrinologist is by now complete. Like any successful drug, RU486 has become the prototype of a number of analogues which are claimed to be either more active or more dissociated. The literature (mainly patients) has been searched for available data on abortive activities, and some as yet unpublished results on RU compounds have been included. It appears that a number of compounds are both more active than RU486 on a dose basis in animal studies and more dissociated in relation to a possible antiglucocorticoid activity. In addition, hydrosoluble compounds suitable for i.v. injection are available for possible development. In a longer term perspective, it cannot be excluded that potential non-steroidal antiprogestins could present additional advantages over steroidal compounds, in particular improved receptor specificity and/or reduced susceptibility to receptor mutation.