A 24-year-old woman with polycystic ovary syndrome presents with hirsutism. She is prescribed spironolactone. The primary mechanism by which spironolactone reduces androgen-mediated hirsutism is:

• A Inhibition of 5-alpha reductase conversion of testosterone to DHT
• B Competitive blockade of the androgen receptor ✓
• C Suppression of ovarian androgen synthesis via inhibition of 17-alpha hydroxylase
• D Increased hepatic synthesis of sex hormone binding globulin

Explanation

Spironolactone acts as a competitive antagonist at the androgen receptor, blocking the peripheral action of androgens on hair follicles. It also has weak inhibitory effects on 21-hydroxylase and can modestly increase SHBG, but its primary anti-androgenic action in hirsutism is androgen receptor blockade. Finasteride, by contrast, works by inhibiting 5-alpha reductase as described in option A.

Reference: Katzung Basic and Clinical Pharmacology, 15th ed.

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