The anti-progestational activity of mifepristone results from competitive interaction with progesterone at progesterone-receptor sites. Based on studies with various oral doses in several animal species (mouse, rat, rabbit and monkey), the compound inhibits the activity of endogenous or exogenous progesterone. The termination of pregnancy results. In the treatment of Cushing's syndrome, Mifepristone blocks the binding of cortisol to its receptor. It does not decrease cortisol production but reduces the effects of excess cortisol, such as high blood sugar levels.
Mifepristone is a synthetic steroid with antiprogestational effects indicated for the medical termination of intrauterine pregnancy through 49 days' pregnancy. Doses of 1 mg/kg or greater of mifepristone have been shown to antagonize the endometrial and myometrial effects of progesterone in women. During pregnancy, the compound sensitizes the myometrium to the contraction-inducing activity of prostaglandins. Mifepristone also exhibits antiglucocorticoid and weak antiandrogenic activity. The activity of the glucocorticoid dexamethasone in rats was inhibited following doses of 10 to 25 mg/kg of mifepristone. Doses of 4.5 mg/kg or greater in human beings resulted in a compensatory elevation of adrenocorticotropic hormone (ACTH) and cortisol.
Hepatic. Hepatic, by Cytochrome P450 3A4 isoenzyme to the N-monodemethylated metabolite (RU 42 633); RU 42 698, which results from the loss of two methyl groups from position 11 beta; and RU 42 698, which results from terminal hydroxylation of the 17_propynyl chain.
Nearly all of the women who receive mifepristone will report adverse reactions, and many can be expected to report more than one such reaction. About 90% of patients report adverse reactions following administration of misoprostol on day three of the treatment procedure. Side effects include more heavy bleeding than a heavy manstrual period, abdominal pain, uterine cramping, nausea, vomiting, and diarrhea.