About dutasteridea 5-alpha-reductase inhibitor, in benign prostatic hyperplasia(bph),male baldness.mechanism of action of dutasteridethis is a selective inhibitor of both type 1 and type 2 isoforms of steroid 5alpha-reductase (an intracellular enzyme that converts testosterone to 5alpha-dihydrotestosterone which influences the development of prostate gland). this decreasing level of this hormone relieves the symptoms associated with benign prostatic hyperplasia.indications for dutasteride1. benign prostatic hyperplasia (bph) 2. male pattern baldness