Marked Suppression of Dihydrotestosterone in Men with Benign Prostatic Hyperplasia by Dutasteride, a Dual 5α-Reductase Inhibitor

Dihydrotestosterone (DHT) is the primary metabolite of testosterone in the prostate and skin. Testosterone is converted to DHT by 5α-reductase, which exists in two isoenzyme forms (types 1 and 2). DHT is associated with development of benign prostatic hyperplasia (BPH), and reduction in its level with 5α-reductase inhibitors improves the symptoms associated with BPH and reduces the risk of acute urinary retention and prostate surgery. A selective inhibitor of the type 2 isoenzyme (finasteride) has been shown to decrease serum DHT by about 70%. We hypothesized that inhibition of both isoenzymes with the dual inhibitor dutasteride would more effectively suppress serum DHT levels than selective inhibition of only the type 2 isoenzyme. A total of 399 patients with BPH were randomized to receive once-daily dosing for 24 wk of dutasteride (0.01, 0.05, 0.5, 2.5, or 5.0 mg), 5 mg finasteride, or placebo. The mean percent decrease in DHT was 98.4 ± 1.2% with 5.0 mg dutasteride and 94.7 ± 3.3% with 0.5 mg dutasteri...