|Mifepristone belongs to a group of medicines known as anti-progesterones. Mifepristone is a synthetic steroid with an antiprogestational action as a result of competition with progesterone at the progesterone receptors. Mifepristone acts by blocking progesterone receptors in the uterus and this reduces the effectiveness of the natural hormone progesterone. The anti-progestational activity of mifepristone results from competitive interaction with progesterone at progesterone-receptor sites.
Mifepristone is used medically in humans as an abortifacient, for the chemical abortion of early pregnancy. In the United States it is made by Danco Laboratories under the tradename Mifeprex. During early trials, it was known as RU-486 after its designation at the Roussel Uclaf company. Mifepristone is a white powder, highly soluble in methanol and only poorly soluble in water.
Mifepristone is used alone or in combination with misoprostol (Cytotec) to end an early pregnancy. This drug causes pregnancy to end by blocking the female hormone progesterone. The lack of progesterone makes the uterus shed its lining, which causes bleeding similar to a menstrual period. Progesterone plays an important role in the maintainance of pregnancy such as the successful implantation of the fertilised egg into the wall of the uterus and prevention of uterine contractions during pregnancy. By blocking progesterone receptors in the uterus, mifepristone significantly reduces progesterone levels so that pregnancy cannot be maintained.
Women who are more than seven weeks pregnant should not take mifepristone. Mifepristone is contraindicated in cases of ectopic pregnancy, adrenal failure, hemorrhagic disorders, anticoagulant or corticosteroid therapy. Side effects include an expected amount of abdominal pain and vaginal bleeding, with the possibility of nausea, vomiting and fever. Incomplete termination of a pregnancy would require further intervention by a doctor (such as vacuum aspiration). Mifepristone should never be prescribed in the following situations: chronic adrenal failure, known allergy to mifepristone or to any component of the product, severe asthma uncontrolled by corticosteroid therapy, porphyrias. It must not be used if there are contraindications to the prostaglandins used in conjunction with mifepristone.