VAGINAL CONTRACEPTIVE RINGS

Steroids diffuse through polysiloxone at a constant rate, and steroids placed in the vagina rapidly pass through the vaginal epithelium into the circulation. Combining these principles led to the development of contraceptive vaginal rings (CVR) consisting of various progestins, with and without oestrogen, placed in flexible polysiloxone, doughnut-shaped devices. As occurs with oral contraceptives, the CVRs containing progestin plus oestrogen are left in the vagina for 3 weeks and removed for 1 week to allow withdrawal bleeding, while CVRs releasing a small dose of progestins without oestrogen are left in the vagina continuously for several months. Large-scale, clinical trials were performed with a low dose levonorgestrel-releasing-only CVR by the WHO. At 1 year, continuation rates were about 50 per 100 women with 17.2 per 100 discontinuing for menstrual problems and 4.5 for pregnancy. Two sizes of a CVR containing levonorgestrel and oestradiol were studied in a multinational trial organized by the Population Council. At the end of 1 year, about half the women were continuing with the method, one-quarter had discontinued because of bleeding problems, and pregnancy rates were between 1 and 2 per 100 women. The CVR was well accepted by women and their partners, but because of lowered HDL-cholesterol levels and accelerated atherosclerosis in female monkeys, further development of this formulation was discontinued. Recently, phase 11 clinical trials with CVRs containing combinations of NET-acetate plus ethinyloestradiol and 3-ketodesogestrel plus ethinyloestradiol have been undertaken. These CVRs provide good bleeding control, inhibit ovulation consistently and do not have an adverse effect on serum lipids. Phase III trials with these two types of CVRs will be initiated shortly.