Mifepristone (RU486) is used for medical termination of pregnancy. Beyond its anti-progestational action, it also has clinically relevant effects on which other receptor?

• A Estrogen receptor — it is an antiestrogen synergising with misoprostol for termination
• B Mineralocorticoid receptor — it blocks aldosterone, causing hyperkalaemia and sodium wasting
• C Androgen receptor — it is used as an antiandrogen for prostate cancer at high doses
• D Glucocorticoid receptor — it is a potent antiglucocorticoid, and at high doses used for Cushing syndrome (400–1200 mg/day) it blocks cortisol action at the receptor level ✓

Explanation

Mifepristone is a competitive antagonist at both progesterone receptors (PR) and glucocorticoid receptors (GR), with high affinity for both. At the doses used for Cushing syndrome (600–1200 mg/day, well above the 200–600 mg dose for MTP), mifepristone's GR antagonism blocks cortisol action at target tissues, making it useful for treating hypercortisolism in Cushing syndrome (where pituitary feedback is also disrupted). Its mineralocorticoid receptor antagonism is relatively weak, and it is not an antiestrogen or antiandrogen at clinically used doses.

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

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