mifepriston

Mifepristone, also called RU-486, is a medication that acts as a competitive antagonist of progesterone receptors and, at higher doses, as a glucocorticoid receptor antagonist. By blocking progesterone signaling, it disrupts the lining of the uterus and the support of an early pregnancy, sensitizing the uterus to prostaglandins.

Medical use and administration

Mifepristone is used in combination with a prostaglandin (typically misoprostol) to terminate early intrauterine pregnancy. In a common regimen, oral mifepristone is given first, followed by misoprostol after 24 to 72 hours to induce uterine contractions and expel the pregnancy. The allowable gestational age for medical abortion with this combination varies by country and guideline, but it is generally restricted to the first trimester. The treatment is provided under medical supervision with appropriate follow-up to confirm completion and rule out ongoing pregnancy or complications.

Mechanism of action

The drug’s primary effect is progesterone receptor antagonism, which deprives the developing pregnancy of hormonal support and leads to decidual breakdown. Its glucocorticoid receptor antagonism can contribute to a broader spectrum of endocrine effects, though the clinical focus in abortion is progesterone blockade paired with prostaglandin-induced uterine activity.

Safety and contraindications

Common side effects include vaginal bleeding, cramping, nausea, vomiting, diarrhea, fatigue, and headache. Serious adverse events are uncommon but can include heavy bleeding, infection, or an incomplete abortion requiring medical intervention. It is contraindicated in cases of suspected ectopic pregnancy and should be used only in appropriate clinical settings with follow-up to ensure complete termination.

Regulatory status and other uses

Mifepristone has been approved for use in many countries for first-trimester abortion, with protocols varying by jurisdiction. In addition to obstetric use, it has glucocorticoid receptor antagonism and is approved in some places for treatment of hypercortisolism (Cushing’s syndrome) in adults, reflecting its broader endocrine activity.