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ADVANCES IN CONTRACEPTION. 1990 Sep; 6(3):169-76.Clinical trials of vaginal rings containing progestins or ethinyl estradiol and progestins by WHO, the Population Council and private firms are reviewed. Contraceptive steroids can be formulated into Silastic vaginal rings because they are released continuously from this material (zero-order kinetics). Vaginal rings have the advantage of avoiding the 1st pass effect on the liver, as well as self- administration, unrelated to the timing of coitus and regulation of withdrawal bleeding with removal for 7 days per cycle. The shell vaginal ring, with an inert core, a layer of Silastic containing the progestogen, and an outer Silastic layer is designed to regulate release by the thickness of the outer layer. The WHO tested rings releasing 200 mcg norethisterone/day resulting in too many menstrual side effects; and 50 mcg/day with too high a failure rate. A ring releasing 20 mcg levonorgestrel is expected to perform well. The Population Council designed rings releasing 152 mcg ethinyl estradiol and 252 mcg levonorgestrel, and 183 mcg ethinyl estradiol and 293 mcg levonorgestrel. These resulted in pregnancy rates of 2/100 woman years, and continuation rates of 50%, but unacceptably adverse lipid effects. Women discontinued for vaginal symptoms. Compared to a similar combined oral pill, the rings offered no advantage. WHO subsequently introduced a ring releasing 20 mcg levonorgestrel: efficacy was 3.8 and continuation over 50%. A new segmented ring with desogestrel is causing fewer androgenic effects and bleeding complaints. Another ring in current trials gives off 120 mcg desogestrel and 30 mcg ethinyl estradiol with no pregnancies and good acceptability in 100 women to date. Availability of Silastic material and quality control in manufacture are seen as obstacles to overcome for mass production of these vaginal rings.
Contraception. 1982 Mar; 25(3):231-41.A randomized, controlled, clinical trial comparing 6 combined oral contraceptives (OCs) with 50 mcg or less of ethinyl estradiol was undertaken in 10 WHO Collaborating Centers for Clinical Research in Human Reproduction. A total of 2430 women entered the trial and were observed for 28,077 woman-cycles. All low-dose combined OCs demonstrated equivalent efficacy with 1-year pregnancy rates of 1-6%. However, discontinuation rates for medical reasons differed significantly between the treatment groups with the preparation containing 20 mcg ethinyl estradiol and that containing 400 mcg norethisterone acetate being associated with higher discontinuation rates due to bleeding disturbances. Even among the preparations which did not differ in discontinuation rates, the reasons for discontinuation did differ. Women receiving norethisterone preparations tended to discontinue because of bleeding disturbances while those receiving the levonorgestrel-containing preparations tended to discontinue because of complaints of nausea and vomiting. (author's)