Segesterone acetate serum levels with a regression model of continuous use of the segesterone acetate/ethinyl estradiol contraceptive vaginal system.

OBJECTIVE: To predict serum segesterone (SA) and ethinyl estradiol (EE) levels after 364 days of hypothetical continuous use (without removal) of a cyclic contraceptive vaginal system (CVS) containing 0.15 mg SA and 0.013 mg EE. STUDY DESIGN: We used pharmacokinetic (PK) data (n = 37) from a multicenter, open-label, nonrandomized study of healthy women (18-38 years) that used the CVS for 13 cycles in a 21 days-in/7 days-out regimen to develop a linear regression model to predict daily serum SA and EE levels for 364 days of continuous CVS use. We then determined residual SA/EE levels in vitro from 18 randomly chosen CVS used by women who completed 13 cycles. Serum SA and EE levels were also predicted for 364 days of continuous CVS use in another in vitro study. RESULTS: After a hypothetical 364 days of continuous CVS use, we predicted daily mean serum levels to be 184 pmol/L (95% confidence interval [CI], 102‒332 pmol/L) for SA and 43 pmol/L (95% CI, 19‒95 pmol/L) for EE. We did predict that serum EE levels would not accumulate over time. Residual SA and EE in the CVS were 60% and 80% of the original load after 13 cycles, respectively. CONCLUSION: The predicted serum SA level after 364 days of hypothetical continuous CVS use was comparable to reported levels at which no pregnancy occurred (>100 pmol/L), showing the potential of the CVS for one year of continuous use. Clinical trials on continuous CVS use are planned. IMPLICATIONS: Based on statistical modeling, the long-term, user-controlled contraceptive vaginal system containing segesterone acetate and ethinyl estradiol may have the potential to provide effective pregnancy prevention if used continuously (without removal) for one year. Further investigation is warranted.