Effect of once weekly administration of mifepristone on ovarian function in normal women

The effects of mifepristone on ovarian function during a once weekly oral administration regimen were studied in nine healthy women. Each received 25 mg mifepristone on cycle days 3, 10, 17, and 24. Ovulation, as documented by hormonal measurements and ultrasonography, was inhibited during treatment in five subjects, with a midcycle surge of luteinizing hormone and ovulation occurring 6-18 days after the last pill was administered in four of the five subjects. These five treatment cycles were prolonged 9-26 days. The other four subjects had normal cycles as judged by serum hormone levels, ultrasonography, and cycle length. All nine subjects had delayed endometrial growth as indicated by ultrasonography. There was a significant correlation between concentrations of serum mifepristone (10 h and 58 h) and alpha 1-acid glycoprotein, the protein to which mifepristone binds in circulation. Response to mifepristone did not depend on its circulating levels. We conclude that once weekly administration of 25 mg mifepristone can interfere with normal follicular development and function, but the inhibition of ovulation was inconsistent.