The antiprogesterone steroid, RU 486 (mifepristone).

ABSTRACT

PIP: RU 486, developed from norethisterone by Roussel Manufacturers, represents the first effective antiprogestogen. Although RU 486 binds strongly to the progesterone receptor, it inhibits progestogenic effects, making this a receptor blocking drug. When administered in the late follicular phase of the menstrual cycle, RU 486 has been shown to delay ovulation. In the first half of the luteal phase, RU 486 destroys the corpus luteum. If luteolysis occurs, RU 486 administration is followed by a single bleeding episode; in the absence of luteolysis, a second bleeding episode occurs several days later in conjunction with the disappearance of the corpus luteum. No clinical use has been found for RU 486's ability to delay ovulation, and luteal phase administration of RU 486 is not yet an effective means of menstrual induction. RU 486 has been most successfully used to induce early abortion, either alone or in combination with a prostaglandin. In most recent study of RU 486, involving 75 women, complete abortion was achieved in 95% of cases. Animal studies have found RU 486 to be effective as a cervical ripening agent and in the induction of labor. They further suggest that the drug can accelerate lactation, prevent breast cancer proliferation, minimize the need for salpingectomy in ectopic pregnancy, and treat Cushing syndrome and glaucoma. To date, there has been no evidence of any teratogenic or antiglucocorticoid side effects. However, more research is needed to confirm the safety of RU 486 for use in viable human pregnancies.