Mifepristones relative binding affinity at the progesterone receptor is more than twice that of progesterone, its relative binding affinity at the glucocorticoid receptor is more than three times that of dexamethasone and more than ten times that of cortisol. Its relative binding affinity at the androgen receptor is less than one-third that of testosterone, and it does not bind to the estrogen receptor or the mineralocorticoid receptor.Mifepristone as a regular contraceptive at 2 mg daily prevents ovulation (1 mg daily does not). A single preovulatory 10-mg dose of mifepristone delays ovulation by three to four days and is as effective an emergency contraceptive as a single 1.5-mg dose of the progestin levonorgestrel.In women, mifepristone at doses greater or equal to 1 mg/kg antagonizes the endometrial and myometrial effects of progesterone. In humans, an antiglucocorticoid effect of mifepristone is manifested at doses greater or equal to 4.5 mg/kg by a compensatory increase in ACTH and cortisol. In animals, a weak antiandrogenic effect is seen with prolonged administration of very high doses of 10 to 100 mg/kg.In medication abortion regimens, mifepristone blockade of progesterone receptors directly causes endometrial decidual degeneration, cervical softening and dilatation, release of endogenous prostaglandins, and an increase in the sensitivity of the myometrium to the contractile effects of prostaglandins.
Mifepristone, also known as RU-486, is a medication typically used in combination with misoprostol to bring about a medical abortion during pregnancy and manage early miscarriage. This combination is 97% effective during the first 63 days of pregnancy. It is also effective in the second trimester of pregnancy. Effectiveness should be verified two weeks after use. It is taken by mouth.Common side effects include abdominal pain, feeling tired, and vaginal bleeding. Serious side effects may include heavy vaginal bleeding, bacterial infection, and birth defects if the pregnancy does not end. If used, appropriate follow up care needs to be available. Mifepristone is an antiprogestogen. It works by blocking the effects of progesterone, making both the cervix and uterine vessels dilate and causing uterine contraction.Mifepristone was developed in 1980 and came into use in France in 1987. It became available in the United States in 2000. It is on the World Health Organizations List of Essential Medicines. Mifepristone was approved by Health Canada in 2015 and became available in Canada in January 2017. Cost and availability limits access in many parts of the developing world. Medical uses
Abortion
Mifepristone followed by a prostaglandin analog (misoprostol or gemeprost) is used for medical abortion. Medical organizations have found this combination to be safe and effective. Guidelines from the Royal College of Obstetricians and Gynaecologists describe medication abortion using mifepristone and misoprostol as effective and appropriate at any gestational age.