New delivery systems in contraception: vaginal rings.

Vaginal rings, made of soft flexible silicone rubber, for delivery of contraceptive hormones are currently gaining clinical acceptance. This method provides extended release of hormones, which are implanted in the core of the ring and slowly disseminate into vaginal tissue. Although formulations and sizes vary, most rings are approximately 58 mm in diameter with a cross-section of 8.4 mm. Depending on the type of ring used, prolonged hormone release may occur from 3 weeks to 1 year. Advantages of the vaginal ring method are that it is user controlled, does not interfere with intercourse, does not require daily intake of a pill, and allows continuous delivery of a low dose of steroids. The Population Council has developed a progesterone-releasing ring, which is currently on the market in Chile and Peru for contraception in breastfeeding women. This ring may be effective for progesterone therapy during in vitro fertilization as well. A contraceptive ring releasing very low doses of the potent progestin Nestorone (Population Council, New York, NY) for 6 to 12 months is also under investigation. The optimal ring formulations, however, contain hormone combinations that provide excellent contraceptive efficacy with few side effects and good control of menstrual bleeding. The Food and Drug Administration has recently approved Organon's monthly ring releasing etonogestrel and ethinyl estradiol. The Population Council is developing a 1-year contraceptive ring releasing low doses of Nestorone and ethinyl estradiol. Combination rings are associated with very low pregnancy rates and side effects consistent with those of oral contraceptives.