The mechanism of action of mifepristone is characterised by a competitive blockade of the progesterone receptors in the uterus. Moreover, it increases the sensitivity of the myometrium for prostaglandins in order to cause contractions. Mifepristone itself has no prostagenous effects.
Misoprostol belongs to the group of eicosanoids. Misoprostol is an analogue of prostaglandin E1 and binds to prostaglandin receptors in the uterus activating the smooth muscles.
In case of pregnancy until 49 days, one dose of 200 mg mifepristone followed by a vaginal application of 800 μg misoprostol 24-48 hours later is sufficient to evoke abortion. This treatment can still be applied when abortion is required on medical grounds after the first trimester. However, pharmacological abortion fails in 3% of the cases and then curettage is still necessary.
Adverse effects of pharmacological abortion are pain, nausea, diarrhea and vomiting. Usually the pain is treated with NSAIDs.
What is true about mifepristone? It is...
Extra info: Extra-uterine pregnancy is a contraindication for mifepristone. In addition to being an antiprogestagen, mifepristone is also an antiglucocorticoid and a weak antiandrogen, but not a prostaglandin sysnthesis inhibitor.