Objective: To compare the effect of 5 and 10 mg of mifepristone on uterine leiomyoma size and symptoms, and to measure side effects.
Methods: Forty premenopausal women with large, symptomatic leiomyomata were randomized to receive either 5 or 10 mg of mifepristone daily for 6 months in an open-label study. Uterine volume was measured at bimonthly intervals by sonography. Serum concentrations of hemoglobin levels, follicle-stimulating hormone, and liver enzymes were obtained, and endometrial samples, symptoms, and menstrual bleeding were also assessed.
Results: Nineteen of 20 subjects taking 5 mg and all 20 subjects taking 10 mg completed all 6 months of the study. Mean uterine volume shrank by 48% (P <.001) in the 5-mg group and 49% (P <.001) in the 10-mg group, a nonsignificant difference. Leiomyoma-related symptoms were comparably reduced in both groups. Amenorrhea occurred in 60-65% of both groups. Hemoglobin levels increased by 2.5 g/dL in anemic subjects. The incidence of hot flashes increased significantly over baseline in the 10-mg group but not in the 5-mg group. Simple endometrial hyperplasia occurred in 28% of all subjects, with no difference between groups. No atypical hyperplasia was noted.
Conclusion: Mifepristone in doses of 5 mg or 10 mg results in comparable leiomyoma regression, improvement in symptoms, and few side effects. Further study is needed to assess the long-term safety and efficacy of low-dose mifepristone.