Where next with long-acting steroids?
Potts, D.M.; Siemens, A.J.
Ippf Medical Bulletin 18(3): 2-3
1984
ISSN/ISBN: 0019-0357 PMID: 12266285 Document Number: 227360
A new generation of steroidal contraceptives is undergoing clinical trials or has reached the stage of national drug authority approval. In November 1983, Norplant contraceptive implants were approved for marketing in Finland as a longacting contraceptive. Norplant continues to be evaluated in large-scale clinical trials in a number of developing and developed countries. A continuous low dose of levonorgestrel is released into the woman's blood from 6 small silastic capsules implanted under the skin of the arm. A variation using 2 implants is under study. The implant systemmay be used for up to 5 years. The mechanism of action of levonorgestrel has 3 components: inhibition of ovulation in about 1/2 of cycles, suppression of the endometrium, and alteration of the cervical mucus to make it less permeable to sperm. The annual pregnancy rate is about .5/100 women. Fertility returns rapidly after removal, and the implant system has a good safety profile. The most frequent side effects in the 1st months of use are apparently menstrual irregularity or spotting, but total blood loss may be decreased. The steroid does not influence blood pressure and hasno unfavorable effect on blood lipids. The Population Council, developer of Norplant, is expected to seek US Food and Drug Administration approval on the basis of specific clinical experience. A vaginal ring consisting of a 3-layer ring of silastic containing levonorgestrel and estradiol has also been developed by the Population Council. The 2 hormones are released into the vagina at a constant rate and absorbed into the woman's blood, resulting in inhibition of ovulation. The rings imitate the action of combined oral contraceptives but do not require daily administration. The World Health Organization is also developing a vaginal ring which contains only a progestogen and is worn without a 1-week break in use. A new sustained-release formulation of norethindrone (NET) is entering expanded clinical trials in the US and developing countries. The system consists of biodegradable polymeric microspheres containing NET which are injected intramuscularly as a suspension. Depending on the size of the microspheres the product can provide 30,90, or 180 day contraceptive protect ive with a single dose. The availability of the 3 formulations each with different durations of action will serve the contraceptive needs of varied populations. Most longacting steroidal contraceptives give rise to menstrual irregularities, but they have the convenience of long action and the physiological advantage of low doses delivered directly to the systemic circulation. Use by millions of women for 1-2 decades will be required before they are completely understood.