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Novel vaginal ring effectively prevents unwanted pregnancy

Pearl Toh
17 Apr 2019

A contraceptive vaginal system (Annovera) releasing a combination of segesterone acetate and ethinyl estradiol (SA/EE) effectively inhibits ovulation up to a year even at low systemic levels of SA, reports a review study presented at ENDO 2019.

SA is a synthetic progestin which binds specifically to progesterone receptors. Unlike other combination hormone contraceptives, SA does not bind to sex hormone-binding globulin (SHBG) and shows no activity on the oestrogenic or androgenic pathways.

“We wanted to prove whether the segesterone in combination with the low dose of EE in this unique vaginal system was adequate at inhibiting ovulation and pregnancy as well as providing good cycle control,” said Dr David Archer from Eastern Virginia Medical School in Norfolk, Virginia, US. 

The vaginal ring contraceptive has recently been approved by the US FDA and the presentation at ENDO 2019 was a review of the evidence on serum SA levels required for inhibiting ovulation. [ENDO 2019, abstract OR33-5]

The self-inserted ring has a Pearl Index (which is indicative of failure rate) of 2.98. “This rate means that only about three unintended pregnancies occur per 100 women in a year compared to a Pearl Index of 80 in couples not using a contraceptive method,” explained Archer.

Earlier dose-finding studies of subdermal implants releasing SA showed that the effect of SA on inhibiting ovulation was dose-dependent, with activity on the hypothalamus and/or pituitary at lower plasma SA levels, and a direct effect on the ovaries at higher plasma concentrations. [Fertil Steril 1985;44:20-24; Contraception 1992;45:49-55]

A separate study of subdermal implants which released 45–50 µg SA/day revealed that ovulation was inhibited at plasma SA levels as low as >150 pmol/L. [Contraception 1995;51:33-38]

Data from another study lent further support to the findings above, which demonstrated that all ring-delivered doses of SA (50, 75, 100 µg SA/day) tested — corresponding to SA serum levels of about 125, 200 and 250 pmol/L, respectively — effectively inhibited ovulation starting from as low as serum SA levels of 125 pmol/L. Also, the serum SA was maintained at fairly constant levels throughout the 6-month study, although there was slight decrease over time. [Contraception 2001;63:257-261]

For better cycle control, SA was combined with EE at doses of 50/10, 50/20, 150/15 µg/µg per day, resulting in plasma SA levels of in the range of 200–300 pmol/L, which provided effective ovulation suppression. [Contraception 2005;72:40-45; Contraception 2005;71:122-129]

“The SA release in the current vaginal ring effectively inhibits ovulation, resulting in the high level of contraceptive efficacy for this long-acting, reversible contraceptive,” said Archer.

The success rate of 97 percent with the vaginal ring system is comparable to most effective birth control methods available on the market which were ≥95 percent effective, he pointed out.

“Annovera represents a novel, procedure-free and long-acting reversible contraceptive method that can provide contraceptive benefits for up to one year,” said Archer.

 

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