Endometrial effects of a single early luteal dose of the selective progesterone receptor modulator CDB-2914

Objective: To test potential contraceptive mechanisms of the selective P receptor modulator CDB-2914 in the early luteal phase. Design: Prospective randomized clinical trial. Setting: Clinical research center. Patient(s): Fifty-six women with regular cycles. Intervention(s): Women received a single dose of CDB-2914 (10, 50, or 100 mg) or placebo given after ovulation and within 2 days of the LH surge. Four to 6 days later, a transvaginal ultrasound scan measured endometrial thickness, and an endometrial biopsy specimen was obtained. Main Outcome Measure(s): The endometrium was evaluated by thickness and by immunohistochemical analysis for P-dependent markers; safety laboratory tests were performed, and E₂ and P levels were obtained. Result(s): CDB-2914 caused a significant dose-dependent decrease in endometrial thickness, an increase in glandular P receptors, and a decrease in peripheral node addressins. Estradiol and P levels and menstrual cycle timing were not altered. No adverse effects were observed. Conclusion(s): The alteration in endometrial thickness and P-dependent markers of implantation in the absence of changes in hormone levels and cycle length suggests that CDB-2914 may have contraceptive properties.