Effects of the antiprogesterone RU 486 in normal women. I. Single-dose administration in the midluteal phase

The response to a single oral dose of the antiprogesterone RU 486 was studied in the midluteal phase in 26 normal women. Each subject received a dose between 50 and 800 mg RU 486 on days 6 to 8 after the luteinizing hormone surge and blood samples were taken over the following 48 hours. Another group of five patients received a single oral dose of 200 mg RU 486 and blood sampling was extended for 14 days. Menses were induced in all women but one within 3 days after RU 486 administration. Two distinct patient populations emerged. In nine of the subjects, there was a single bleeding episode and the treatment cycle was significantly shorter (p less than 0.05) than the following cycle. In 16 of these 25 patients a second bleeding episode occurred 19.0 +/- 0.8 days after the luteinizing hormone surge. The total treatment cycle was significantly prolonged (p less than 0.05) when compared with the following cycle. In the group with a single bleeding episode, there was a significant decline in follicle-stimulating hormone, estradiol, and progesterone over the 48-hour sampling period, but there was no change in these values in the group with two bleeding episodes. These two groups could not be separated on the basis of RU 486 dose or serum levels. After the four higher doses, there was a dose-dependent rise in serum prolactin. There were no alterations in mean cortisol values with the three lower doses, but there was a significant increase at 24 and 48 hours after the higher doses. Serum levels of RU 486 were maximal between 1 and 4 hours and the half-life of serum RU 486 was determined to be 24 hours.