Mifepristone (RU-486) is used for medical termination of pregnancy in combination with misoprostol. Its mechanism involves:
- A Direct prostaglandin E2 agonism causing uterine contractions
- B Inhibition of 3-beta-hydroxysteroid dehydrogenase reducing progesterone synthesis in the corpus luteum
- C Competitive antagonism at progesterone receptors causing decidual breakdown and increasing uterine prostaglandin sensitivity ✓
- D GnRH receptor agonism causing downregulation of LH support for the corpus luteum
Correct answer: C. Competitive antagonism at progesterone receptors causing decidual breakdown and increasing uterine prostaglandin sensitivity
Explanation
Mifepristone is a potent competitive antagonist at progesterone receptors (and also glucocorticoid receptors). By blocking progesterone's actions, it causes decidual necrosis (breakdown of the uterine lining supporting the pregnancy), cervical softening, and importantly increases uterine sensitivity to prostaglandins. Misoprostol (PGE1 analog) is given 24–48 hours later to induce uterine contractions that expel the products of conception. The combination achieves >95% efficacy up to 10 weeks.
Reference: KD Tripathi, Essentials of Medical Pharmacology, 8th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.