HORMONAL ANTI-IMPLANTATION AGENTS - ANTIPROGESTINS

Oestrogens and progestogens separately or in combination are able to p revent implantation with high efficiency, thus acting as interceptive agents. Current interceptive medical regimens include high-dose oestro gens, the association of oestrogens with progestogens or progestogens alone, Compounds with antiprogesterone properties, such as RU 486 (mif epristone) or ZK 98734 (lilopristone), also exhibit a strong intercept ive action which, as shown in animal models, is proportional to the do se and the day(s) of administration, Recent clinical studies show that RU 486 can be used successfully for postcoital interception, The regi men applied for this purpose consists of the intake of a single dose o f 600 mg RU 486 within 72 h of a single act of unprotected intercourse , This treatment was found to be highly effective and to have a more f avourably side-effect profile in with the oestrogen-progestogen regime n. However, because of the induced irregularities of the cycle, the mi fepristone regimen, as with the other hormonal methods, should not be used on a regular basis, Currently, all interceptive hormonal regimens are emergency methods, Their occasional use to prevent unwanted pregn ancies may reduce the number of therapeutic abortions, However, the fr equency and extent of their side-effects do not allow for a repeated p ostcoital use after every act of unprotected intercourse, Obviously, t he development of an effective and safe 'morning after pill' requires further basic and clinical investigations.