Mifepristone is a synthetic steroid. It is used medically in humans as an abortifacient, for the chemical termination 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.

It is used in the termination of pregnancies less than sixty-four days from conception. A typical dose is 200 mg orally, followed after 48 hours by 800 µg misoprostol, a prostaglandin analogue, given orally or vaginally. Within four hours of the second dose, it is between 92% and 99% effective (depending on the trial data examined), while as a standalone agent it is approximately 80% effective.

It works by competitive interaction with both endogenous and exogenous progesterone at receptor sites. It also has slight antiglucocorticoid and antiandrogenic effects in larger doses.

Mifepristone is a white powder, highly soluble in methanol and only poorly soluble in water. Its structural name is 11β-[p-(Dimethylamino)phenyl]-17β-hydroxy-17-(1-propynyl)estra-4,9-dien-3-one. Its empirical formula is C₂₉H₃₅NO₂

It 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 ).

The compound was discovered by researchers at Roussel Uclaf of France in 1980 while studying glucocorticoid receptor antagonists. Clinical testing began in 1982. It was first licensed in France in 1988, for use in combination with prostaglandin. Then on October 26 of that year, Roussel Uclaf stated that it would abandon distribution of the drug. It bowed to pressure from the government of France two days later to resume distribution. Mifepristone was approved in a number of other European countries in the 1990s: for example, the United Kingdom approved its use in 1991.

Early research was difficult, as Roussel Uclaf did not seek U.S. approval. It was further interrupted when the first Bush administration banned the importation of mifepristone in 1989. This ban was not reversed until 1993. In 1994, Roussel Uclaf gifted the U.S. drug rights to the Population Council and the drug went on approvable status from 1996. Production was intended to begin through the Danco Group in 1996 but they withdrew briefly in 1997, delaying availability again. It was approved by the U.S. Food and Drug Administration (FDA) in September 2000.

Mifepristone has been investigated in the treatment of Cushing's syndrome and a number of cancers.

External Links

• Commonly asked questions about RU-486 from the education arm of the National Coalition of Abortion Providers