A 55-year-old man with benign prostatic hyperplasia is started on finasteride. The mechanism by which finasteride improves urinary symptoms is best described as:

• A Competitive antagonism at androgen receptors in prostatic smooth muscle
• B Direct relaxation of bladder neck smooth muscle via alpha-adrenergic blockade
• C Suppression of gonadotropin release from the pituitary via negative feedback
• D Inhibition of 5-alpha reductase type II, reducing intraprostatic dihydrotestosterone (DHT) levels ✓

Explanation

Finasteride inhibits 5-alpha reductase type II, blocking conversion of testosterone to DHT in the prostate. DHT is the principal androgen driving prostatic growth. Reducing intraprostatic DHT causes prostate volume reduction over months. It does not block androgen receptors (that is bicalutamide/enazalutamide), suppress gonadotropins (that is GnRH analogues), or block alpha receptors (that is tamsulosin). Dutasteride inhibits both type I and type II 5-alpha reductase.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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