· Dutasteride is a newer cogener of finasteride which inhibits the conversion of testosterone to 5 alpha-dihydrotestosterone (DHT), which is the androgen primarily responsible for the initial development and subsequent enlargement of the prostate gland.
· Testosterone is converted to DHT by the enzyme 5 alpha-reductase, which exists as 2 isoforms, type 1 and type 2. Dutasteride is a competitive and specific inhibitor of both type 1 and type 2 5 alpha-reductase isoenzymes, with which it forms a stable enzyme complex.
Reference: Tripathi K.D., "Essentials of medical pharmacology", Jaypee brothers medical publishers, Seventh edition, New Delhi, page no. 303.