Mifepristone (RU-486) is used for medical termination of pregnancy (MTP) and is always combined with a prostaglandin (e.g., misoprostol). The mechanism of mifepristone is:
- A Inhibition of progesterone synthesis in the corpus luteum, causing luteolysis
- B Selective oestrogen receptor modulation, stimulating uterine contractions
- C Competitive blockade of progesterone receptors, causing decidual necrosis and cervical softening, followed by myometrial sensitisation to prostaglandins ✓
- D Inhibition of HCG secretion from the trophoblast, causing embryo demise
Correct answer: C. Competitive blockade of progesterone receptors, causing decidual necrosis and cervical softening, followed by myometrial sensitisation to prostaglandins
Explanation
Mifepristone is a synthetic 19-norsteroid that competitively antagonises progesterone at its receptor. Progesterone withdrawal causes decidual necrosis, endometrial breakdown, and cervical ripening (softening and dilatation). It also upregulates myometrial prostaglandin receptors and gap junctions, sensitising the uterus to the contractile effects of the subsequently administered misoprostol (a PGE1 analogue). Together, they achieve >95% complete abortion in the first trimester. Mifepristone does not inhibit HCG or progesterone synthesis.
Reference: KD Tripathi, Essentials of Medical Pharmacology, 8th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.