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Mifepristone (or RU-486) is a synthetic, steroidal antiprogestogen and antiglucocorticoid pharmaceutical drug. It is a 19-norsteroid with substitutions at positions C11 and C17 (17β-hydroxy-11β-(4-(dimethylamino)phenyl)-17α-(1-propynyl)estra-4,9-dien-3-one), which antagonizes cortisol action competitively at the receptor level. Mifepristone is a low-efficacy partial agonist of the progesterone receptor used as an abortifacient in the first months of pregnancy, and in smaller doses as an emergency contraceptive. It is also a glucocorticoid receptor antagonist to a lesser extent, and has occasionally been used in refractory Cushing's syndrome (due to ectopic/neoplastic ACTH/cortisol secretion). During early trials, it was known as RU-38486 or simply RU-486, its designation at the Roussel Uclaf company, which designed the drug. The drug was initially made available in France, and other countries then followed—often amid controversy. It is marketed under tradenames Korlym and Mifeprex, according to FDA Orange Book. Mifepristone was the first antiprogestin to be developed and it has been evaluated extensively for its use as an abortifacient. The original target for the research group was the discovery and development of compounds with antiglucocorticoid properties. These antiglucocorticoid properties are of great interest in the treatment of severe mood disorders and psychosis, although a review of published articles was inconclusive on their efficacy, and considered the use of these drugs in mood disorders at 'proof of concept' stage. It is on the WHO Model List of Essential Medicines. ==Medical uses== According to the current RCOG abortion guideline: * All methods of first-trimester abortion carry a small risk of the pregnancy continuing despite the attempt to terminate it. The risk of the pregnancy continuing is around 0.23% for surgical abortions and between 0.1% and 1.4% (depending on the regimen used and the experience of the centre) for medical abortions (abortions induced through drugs instead of surgical procedures). * Medical abortion using mifepristone plus prostaglandin is the most effective method of abortion at gestations of less than 7 weeks. * Conventional vacuum aspirations below 7 weeks have a higher failure rate than at later gestations. Protocols should include examination of the aspirate for the presence of the gestational sac and/or follow-up serum human chorionic gonadotrophin estimation, to ensure abortion completion. * Early vacuum aspiration using a rigorous protocol (which includes magnification of aspirated material and indications for serum βhCG follow-up) may be used at gestations below 7 weeks, although data suggest the failure rate is higher than for medical abortion. * Medical abortion using mifepristone plus prostaglandin continues to be an appropriate method for women in the 7–9 week gestation band. Mifepristone is sold outside the United States by Exelgyn Laboratories as Mifegyne, made in France, and is approved for: #Medical termination of intrauterine pregnancies of up to 49 days gestation (up to 63 days gestation in Britain and Sweden) #Softening and dilatation of the cervix prior to mechanical cervical dilatation for pregnancy termination #Use in combination with gemeprost for termination of pregnancies between 13 and 24 weeks gestation #Labor induction in fetal death ''in utero''〔 Mifepristone is sold in the United States by Danco Laboratories as Mifeprex and is U.S. Food and Drug Administration-approved to terminate intrauterine pregnancies of up to 49 days gestation. Under the FDA-approved regimen, a 600-mg dose is administered by a clinician following a counseling session. Two days later, a clinician administers 400 µg of another medicine, misoprostol, to induce contractions. In European studies, this method terminated 96 to 99% of pregnancies of up to 49 days gestation, but in one large multicenter trial in the United States conducted from September 1994 to September 1995, the efficacy was lower (92%), which the authors of the study suggested may have been due to lack of experience with this method in the United States and/or the design of their study. In Europe and China, an observation period of several hours is required after administration of misoprostol. If expulsion of fetal tissue does not occur during the observation period, surgical abortion is offered. No observation period is required in the United States, but it is strongly recommended. Mifepristone can also be used in smaller doses as an emergency contraceptive; if taken after sex but before ovulation, it can prevent ovulation and so prevent pregnancy. In this role, a 10-mg dose is not as effective as the 600-mg dose, but has fewer side effects. Mifeprex and Mifegyne are only available in 200-mg tablets. A review of studies in humans found that the contraceptive effects of the 10-mg dose were probably due mainly to its effects on ovulation, and not inhibition of implantation, but "the knowledge of the mechanism of action remains incomplete". Treatment with 200 mg of mifepristone changes steroid receptor expression in the Fallopian tube, inhibits endometrial development, and effectively prevents implantation. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「mifepristone」の詳細全文を読む スポンサード リンク
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