Mifepristone (RU-486) is used as a medical abortifacient. Its mechanism involves:
- A Competitive antagonism at progesterone and glucocorticoid receptors, inducing endometrial shedding and sensitising the myometrium to prostaglandins ✓
- B Inhibition of 3-beta-hydroxysteroid dehydrogenase, reducing progesterone synthesis in the corpus luteum
- C Direct stimulation of uterine prostaglandin F2-alpha synthesis causing myometrial contractions
- D Blockade of oestrogen receptors in the uterus, preventing implantation of the blastocyst
Correct answer: A. Competitive antagonism at progesterone and glucocorticoid receptors, inducing endometrial shedding and sensitising the myometrium to prostaglandins
Explanation
Mifepristone is a 19-norsteroid that competitively antagonises progesterone receptors (decidua fails to maintain pregnancy) and glucocorticoid receptors. Progesterone withdrawal leads to endometrial breakdown, increased uterine prostaglandin sensitivity, and cervical softening. It is combined with misoprostol (a PGE1 analogue) 24–48 hours later to complete expulsion via myometrial contractions.
Reference: KD Tripathi, Essentials of Medical Pharmacology, 8th ed.
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Written and medically reviewed by the StethoPrep medical team.