Finasteride and dutasteride both treat benign prostatic hyperplasia. The key pharmacological difference between them is that:
- A Finasteride blocks both isoenzymes while dutasteride blocks only type I
- B Finasteride is a competitive antagonist at the androgen receptor, dutasteride is not
- C Dutasteride blocks both type I and type II 5 alpha-reductase, finasteride blocks only type II ✓
- D Dutasteride reduces serum DHT by about 70 percent, finasteride by over 95 percent
Correct answer: C. Dutasteride blocks both type I and type II 5 alpha-reductase, finasteride blocks only type II
Explanation
Type II 5 alpha-reductase predominates in prostate and genital tissue, and finasteride selectively inhibits it, lowering serum dihydrotestosterone by about 70 percent. Dutasteride inhibits both type I and type II isoenzymes, lowering serum DHT by more than 95 percent. Both drugs leave the androgen receptor untouched, which distinguishes them from antiandrogens like flutamide, eliminating option B. The percentage figures in option D are reversed, making it a strong distractor for careless readers.
Reference: Katzung Basic and Clinical Pharmacology, 15th ed.
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