Abstract

PIP: The introductory presentation for a session on antiprogestins summarizes the action of RU 486 relating to its use as a contragestive agent. RU 486, or mifepristone (Roussel-Uclaf), is a progestin analogue resembling norethindrone with a longer 17-alpha side chain and a 11-beta phenyl group that confers the progesterone antagonist activity. It binds the progesterone receptor with a half-life of about 20 hours. Since progesterone receptors are only located in a few tissues, notably the decidualized endometrium and the corpus luteum, its action can be targeted. RU 486 interrupts the cycle regardless of whether fertilization occurred. A single 600 mg dose arrests over 80% of pregnancies up to 41 days, then a decreasing proportion, down to 60% at 10 weeks, due to a greater chance of incomplete evacuation. There have been no recorded side effects in 4000 trails. The effect of prostaglandins is magnified when progesterone action is suppressed. 400 trials have confirmed that over 98% successful termination of pregnancy can be obtained if 600 mg RU 486 is followed by 1 mg synthetic prostaglandin 36 hours later. RU 486 has also tested successfully for delivery of dead fetuses, cervical dilation, a postcoital contraceptive, and as an antiglucocorticoid agent. It has been submitted to the French Ministry of Health, and will probably be approved for marketing in 1988. Clinical trials are underway in 15 countries. This drug is a useful contragestive agent, active in the beginning of the continuum of pregnancy, and may defuse the abortion issue.