Abstract The novel, ring-shaped, contraceptive vaginal system (CVS; Annovera™), contains 103 mg of SA and 17.4 mg of EE, and delivers a mean dose of SA 0.15/EE 0.013 mg/day. The CVS was designed to last thirteen cycles in a 21 day-in/7 day-out regimen. Objectives of these analyses were to determine the amount of SA/EE remaining in the CVS after 13 cycles of use and to estimate the SA level in serum after 1 year of continuous use. Residual SA/EE levels from CVS used by women (n=18) for 13 cycles of 21/7 regimen in a phase 3 clinical trial were further analyzed in vitro. Hypothetical SA level in serum after 1 year of continuous use was estimated using data from 39 women who participated in a 13-cycle pharmacokinetic study of the 21/7 CVS regimen. The serum data were used to construct a statistical model for the change in serum SA concentrations from cycle 1 to cycle 13. The data from each individual subject was modeled to estimate the serum SA level based on days of use. Each subject’s model was then used to estimate the serum SA level after 364 days of continuous CVS use. The average of all 364-day values from valid models was then calculated. After 13 cycles of a 21/7 regimen, the amount of SA/EE remaining in the CVS was 61.7 mg/14.0 mg (60%/80% of the original SA/EE load), which established the release of 0.15 mg SA and 0.013 mg EE per day for a total of 273 days. The model predicted that the mean serum SA level after 364 days of continuous use was 71 pmol/L with a lower limit of the 90% CI of 52 pmol/L. A high percentage of SA/EE remained in the CVS after 13 cycles of use. Serum SA levels predicted by the model following 1 year of continuous use were similar to those previously observed (mean 73 pmol/L) at 1 year in a SA silicone implant trial in which there were no reported pregnancies at 1 year (Sivin et al, Contraception. 2004;69:137-144). No pregnancy or PK data with continuous use of the CVS is available at this time. Further study on the continuous use of the CVS is warranted.