A 62-year-old man with benign prostatic hyperplasia is prescribed finasteride. After 6 months of therapy, his prostate volume decreases. The mechanism of finasteride in BPH involves inhibition of which specific enzyme?

• A Type I 5-alpha reductase
• B 17,20-lyase (CYP17A1)
• C Type I and II 5-alpha reductase equally
• D Type II 5-alpha reductase ✓

Explanation

Finasteride selectively inhibits type II 5-alpha reductase, the isoform predominant in the prostate and responsible for converting testosterone to dihydrotestosterone (DHT). This reduces intraprostatic DHT by approximately 70%, causing prostate shrinkage. Dutasteride inhibits both type I and type II isoforms. This isoform selectivity is a distinguishing pharmacological feature tested in exams.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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