Why does RU486 fail to prevent implantation despite success in inducing menstruation?
Li, T.C.; Lenton, E.A.; Dockery, P.; Rogers, A.W.; Cooke, I.D.
Contraception 38(4): 401-406
1988
ISSN/ISBN: 0010-7824 PMID: 3208514 DOI: 10.1016/0010-7824(88)90081-9Document Number: 359234
To see why RU-486, given in luteal phase, induces menstruation but does not always prevent pregnancy, daily progesterone assays and 3 endometrial biopsies were taken from 2 volunteers who received a single dose. Progesterone was assayed by direct radioimmunoassay from saliva samples. The 1st subject was a 36-year old multipara who took a single oral dose of 150 mg RU-486 on Day 4 after the LH surge. She menstruated apparently normally 2 days later, and again 10 days after RU-486, at the expected time of menstruation. Her endometrial biopsy resembled secretory phase, and her progesterone profile did not indicate luteolysis. The 2nd volunteer was a 38-year old multipara. She took 75 mg RU-486 on Day 6 after her LH surge, and had apparently normal menses 2 days later. The endometrial histology was suggestive of menstruation, and the progesterone profile had fallen to baseline, indicating luteolysis. Menstruation did not recur at the normal time. In this woman who had complete shedding of the endometrium, RU-486 had been taken later in the luteal phase, and in a smaller dosage.