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CONTRACEPTION. 1994 Apr; 49(4):347-59.The World Health Organization [WHO] Special Programme of Research, Development and Research Training in Human Reproduction has coordinated the developmental strategy of combined once-a-month injectable contraceptives. The strategy consists of the selection, based on pharmacokinetic data, of appropriate long-acting progestin-estrogen combinations to develop at least 2 sustained-release formulations; assessment of safety and effectiveness of these formulations in clinical research facilities; and their evaluation at field level through service facilities of national family planning programs. WHO Collaborating Centers were involved in selecting the estrogen-progestogen combinations, ratios, and dose schedules. Research has found at least 3 combined once-a-month injectable contraceptives that demonstrate acceptable pharmacokinetic and pharmacodynamic profiles. 2 safe and effective once-a-month contraceptive formulations (Cyclofem and Mesigyna) can join the existing choice of contraceptive methods. WHO expects more improvement in the design of optimal estrogen/progestin injectables in the 1990s.
British Journal of Family Planning. 1990 Jan; 15(4 Suppl):27-9.The long-acting injectable contraceptives, once-a-month injectables, vaginal rings, and implants, either in use or being clinically tested, are reviewed briefly. About 6 million women now use injectables, 4 million use Depo-Provera, and 1 million use norethisterone enanthate (NET-EN) in a once-monthly schedule. Other once-monthly injectables are being developed by WHO, such as a dihydroxy-progesterone acetophenide-estradiol enanthate being tested in Mexico. These injections are highly effective and acceptable, despite frequency, because they cause regular withdrawal bleeding. Other combinations already tested by WHO are HRP 102 (norethisterone enanthate 50 mg-estradiol valerate 5 mg), and HRP 112 (depo-medroxyprogesterone acetate 25 mg-estradiol cypionate 5 mg). Continuation rates for these methods were 64.5 and 63.2%. Lower doses were not as effective in cycle control. Depo-Provera (depo- medroxyprogesterone acetate, DMPA) is available in 85 countries, and accounts for 65% of injectables, while NET-EN is available in over 40 countries and makes up 15%. Recent studies with DMPA have shown that efficacy can be affected by variations in particle size of the microcrystals, as well as by the population using it. Vaginal rings containing levonorgestrel have reached Phase II trials; failures have been reported due to inconsistent quality. Besides the well-known Norplant, an implant called Capronor is being developed. It is a polycaprolactone tube 4 cm long containing levonorgestrel in ethyl oleate vehicle. IT has a zero order release and biodegrades after 2 years.
In: Zatuchni GI, Labbok MH, Sciarra JJ, eds. Research frontiers in fertility regulation. Hagerstown, Maryland, Harper and Row, 1980. 213-29. (PARFR Series on Fertility Regulation)The systems-engineering approach to delivery of long-term contraception can involve the use of matrix devices for contraceptive steroids from which the steroid is released at a controlled rate over a prolonged period of time after a single administration. The concept of system design principles in contraceptive delivery is explained. In 1973, WHO organized a task force on long-acting systemic agents for fertility regulation. This is the report on a WHO-sponsored project to incorporate the basic design principles of a long-acting system into the design of an injectable particulate contraceptive system. The initial requirements included: 1) provision by a single administration of continuous controlled release of NET (norethisterone) for at least 6 months; 2) injection-administered carrier; 3) biodegradable carrier; 4) no carrier-induced side effects at the site of the injections; 5) complete disappearance of all components from the injection site; 6) a flexible system as to dose and duration to accommodate individual needs; and 7) reversibility of treatment. Experimental data so far satisfy the 1st 6 requirements. The injectable particulate system cannot be made reversible. Aspects for future research in this area are mentioned.