Mifepristone (RU 486): current knowledge and future prospects.

Mifepristone (RU 486) has received recent attention for its effects as an abortifacient. Mifepristone has not yet been approved for use in the United States. The Food and Drug Administration issued an "approvable letter" in September 1996, but mifepristone will not be available in the United States until a new manufacturer is found. Experience with mifepristone is extensive in Europe, and there have been retrospective studies and large, controlled clinical trials of its efficacy. It is most efficacious when administered to women who are less than 8 weeks pregnant, in a single 600-mg oral dose followed 48 hours later by administration of intravaginal misoprostol. This regimen has a success rate of 98%, as do most surgical abortive procedures. The most frequent adverse effect is painful contractions, which occur in up to 93% of women, with oral analgesia required in as many as half the cases. Large-scale surveys of women who elected medical abortion reported high patient satisfaction. Mifepristone is likely to have additional clinical uses. Researchers are exploring mifepristone's potential uses in cervical ripening and labor induction; contraception; delivery after intrauterine demise; treatment of breast cancer, unresectable meningioma, and prostate cancer; amelioration of endometriosis; and management of Cushing syndrome.