Proscar Mechanism of Action

PROSCAR (finasteride, MSD), a synthetic 4-azasteroid compound, is a specific inhibitor of Type II 5α-reductase, an intracellular enzyme which metabolizes testosterone into the more potent androgen dihydrotestosterone (DHT). In benign prostatic hyperplasia (BPH), enlargement of the prostate gland is dependent upon the conversion of testosterone to DHT within the prostate. PROSCAR is highly effective in reducing circulating and intraprostatic DHT. Finasteride has no affinity for the androgen receptor.
In the PROSCAR Long-Term Efficacy and Safety Study (PLESS), the effect of therapy with PROSCAR on BPH-related urologic events (surgical intervention [e.g., transurethral resection of the prostate and prostatectomy] or acute urinary retention requiring catheterization) was assessed over a 4-year period in 3016 patients with moderate to severe symptoms of BPH. In this double-blind, randomized, placebo-controlled multicenter study, treatment with PROSCAR reduced the risk of total urologic events by 51% and was also associated with a marked and sustained regression in prostate volume, and a sustained increase in maximum urinary flow rate and improvement in symptoms.