[RU 486: current and potential indications. Great expectations and strong resistance]

RU 486 is the code name for mifepristone, a 19-norsteroid first synthesized in 1980. Its chemical structure is similar to progesterone and progesterone derivatives. The difference lies in an 11 beta ring substitution which results in high affinity for progesterone and cortisol receptors. Once linked to the receptor, RU 486 temporarily blocks the action of the corresponding hormone. In vitro and in vivo, RU 486 has a powerful anti-progesterone and anti-glucocorticoid effect and a less powerful but nevertheless important anti-androgen effect. The essential clinical application for RU 486 involves its anti-progesterone effect, currently used in several indications including voluntary pregnancy termination and preparation for the prostaglandin action used to induce labour in interrupted pregnancies. Potential indications have been suggested for preparing the cervix for endo-uterine manoeuvres, induction of labour in term pregnancy and contraception. Other potential indications in gynaecology include breast cancer, endometriosis and uterine fibroma. Meningioma and Cushing's syndrome would be further indications. How far will we go with RU 486? All will depend on the social and economic resistance to the drug and to an even greater extent on ethical considerations. The strength of the anti-RU 486 lobby may well dampen the development of non-contraception indications for this effective anti-progesterone agent.