Mifepristone (RU486) causes cervical ripening and myometrial sensitisation to prostaglandins primarily by:

• A Directly stimulating oxytocin receptors on myometrium
• B Blocking endometrial progesterone receptors, withdrawing progesterone-mediated uterine quiescence ✓
• C Inhibiting 17β-hydroxysteroid dehydrogenase, reducing local progesterone biosynthesis
• D Upregulating endometrial COX-2, increasing prostaglandin E2 synthesis de novo

Explanation

Mifepristone is a competitive antagonist at progesterone receptors (and glucocorticoid receptors). Blockade of endometrial progesterone receptors withdraws progesterone-mediated uterine quiescence, promotes decidual breakdown, sensitises myometrial cells to the contractile effects of prostaglandins, and upregulates oxytocin receptors. It is used alone or followed 24–48 h later by misoprostol (PGE1 analogue) for medical termination of pregnancy.

Reference: KD Tripathi, Essentials of Medical Pharmacology, 8th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.