THE USE OF PROGESTERONE ANTAGONISTS IN COMBINATION WITH PROSTAGLANDINFOR TERMINATION OF PREGNANCY

Antiprogestin alone is not sufficiently effective in terminating early pregnancy to be clinically useful. The only exception seems to be imm ediate post-ovulatory administration which inhibits endometrial develo pment to an extent that prevents implantation of the fertilized ovum. During early pregnancy the uterus is inactive. Treatment with antiprog estin with result in an increased uterine contractility and a signific ant increase of myometrial sensitivity to prostaglandin. The effect is probably mainly due to the release of the inhibitory effect of proges terone. Antiprogestin not only activates the uterus, it also causes a ripening of the cervix. The combination of RU486 and either vaginal ad ministration of gemeprost or i.m. injections of nalador provide a safe and effective medical abortion in the first 8 weeks of pregnancy. Rec ent clinical studies indicate that it may be possible to replace the p rostaglandin analogues in current use by the orally active analogue mi soprostol. Misoprostol is inexpensive and stable at room temperature a nd would facilitate the provision of medical abortion with mifepriston e. Experimental data also indicate that a combination of RU486 and mis oprostol may be developed into an effective once-a-month late luteal m ethod to regulate fertility. Pre-treatment with RU486 is also useful i n later stages of gestation. A combination of RU486 and the vaginal ad ministration of gemeprost is a highly effective, safe and simple non-i nvasive method for terminating both early and late second trimester pr egnancy.