Progestin-only contraceptive rings

Several progestin-only long acting contraceptives are currently available i n the form of implants or injectables. Vaginal rings are another contracept ive option in the final stages of development. These steroid-containing pol ymer rings are placed in the vagina, providing relatively constant drug rel ease, thus allowing for lower effective doses. Vaginal rings have the advan tage of being user-controlled and non-provider dependent, and their use is non-coital related. The first clinical study with medroxyprogesterone aceta te vaginal rings was published in 1970. Since then numerous clinical trials testing different steroids and doses have followed. A large Phase III mult icenter clinical trial with a levonorgestrel ring, releasing 20 mug/day, wa s coordinated and sponsored by WHO. The cumulative one-year pregnancy rate was 4.5%. The principal reasons for discontinuation were menstrual disturba nces (17.2%), followed by frequent expulsion of the ring (7.1%), and vagina l symptoms (6.0%). The finding of erythematous lesions in the vagina in som e women has led to the development of a more flexible device. Collaboration with industry should facilitate the manufacture of a redesigned levonorges trel ring with a higher release rate. The Population Council is also develo ping a vaginal ring containing Nestorone((R)) for 6 months of continuous us e, Ovulation inhibition was achieved in over 97% of the segments studied, w ith rings releasing either 50, 75, or 100 mug/day. No pregnancies occurred in women using the low-dose ring, while one pregnancy each occurred in the intermediate- and high-dose ring groups for a 6-month cumulative pregnancy rate of 0.0, 1.9, and 2.1%. Bleeding irregularities were common. Nestorone is orally inactive; therefore this ring is also excellent for use in lactat ing women. (C) 2000 Elsevier Science Inc. All rights reserved.