Late luteal phase administration of RU486 for three successive cycles does not disrupt bleeding patterns or ovulation

RU486, a 19-nor steroid, binds with high affinity to the receptors for progesterone and glucocorticoids, blocking the actions of these hormones on their target tissues. We conducted studies to determine whether RU486 administered at the end of the luteal phase would disturb the menstrual rhythm, ovulation, or hormonal parameters in the treatment and post-treatment cycles. The first study was done in six surgically sterilized women during two consecutive cycles. RU486 [17 beta-hydroxy-11 beta-(4-dimethylaminophenyl)17 alpha-(1-propynyl)estra-4,9-dien-3-one; 100 mg/day] was given for 4 consecutive days, commencing on days 23-27 of the first cycle. Menstrual bleeding occurred by the second day of RU486 administration in all women and was indistinguishable from their usual bleeding pattern. The onset of this bleeding was advanced by RU486 administration, since it entailed shortening of the luteal phase with prolongation of the following follicular phase. Serum LH, FSH, estradiol, and progesterone levels were normal in five of the six women in both the treatment and posttreatment cycles. The second study was conducted in 10 women who were not exposed to the risk of pregnancy. RU486 (100 mg/day) was given for 4 consecutive days, commencing 4 days before their expected menses for 3 successive cycles, preceded and followed by 2 placebo-treated cycles. Bleeding patterns were indistinguishable during the RU486 and placebo cycles. Late luteal phase administration of RU486 consistently produced menstrual bleeding within 1-3 days of drug administration. Daily early morning urinary LH excretion in 6 women and estrone glucuronide and pregnanediol glucuronide excretion in 5 women during both placebo and RU486 cycles were consistent with luteinization, suggesting ovulation and appropriate corpus luteum function. We conclude that RU486 has no major effect on menstrual cycle events if given at the time of the natural progesterone withdrawal that occurs before menses in nonpregnant women.