Mifepristone acts as a competitive antagonist at progesterone receptors. When used for medical termination of pregnancy, it causes sensitisation of the uterus to which subsequent drug?

• A Ergometrine, a dopamine receptor agonist causing uterine contraction
• B Misoprostol (PGE1 analogue), causing cervical ripening and uterine contractions via EP and FP prostaglandin receptors ✓
• C Oxytocin directly, as progesterone receptor blockade upregulates oxytocin receptors
• D Methotrexate, which inhibits trophoblast folate metabolism

Explanation

Mifepristone blocks progesterone receptors in the decidua, causing decidual breakdown, cervical softening, and upregulation of myometrial prostaglandin receptors (EP and FP subtypes). This sensitises the uterus to the subsequent action of misoprostol (PGE1 analogue), which binds prostaglandin receptors to cause cervical ripening (softening and dilation) and intense uterine contractions, expelling the conceptus. The combination is 95–97% effective in the first trimester. Oxytocin receptor upregulation (option C) also occurs but is not the basis for the misoprostol combination.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.