Drug insight: 5 alpha-reductase inhibitors for the treatment of benign prostatic hyperplasia

Benign prostatic hyperplasia (BPH) is a common problem among older men, which is characterized by an enlarged prostate, lower urinary tract symptoms, and decreased flow of urine. It is a progressive disease that can lead to complications such as acute urinary retention (AUR) or a need for BPH-related surgery in some men. Dihydrotestosterone is the primary androgen involved in both normal and abnormal prostate growth and 5 alpha-reductase inhibitors (5ARIs) inhibit the conversion of testosterone to dihydrotestosterone. There are two 5ARIs licensed for the treatment of BPH; dutasteride, which inhibits both type 1 and type 2 isoenzymes of 5 alpha reductase, and finasteride, which inhibits the type 2 isoenzyme. Both 5ARIs have been shown to decrease prostate volume, improve urinary flow and lower urinary tract symptoms and reduce the risk of AUR and BPH-related surgery. The prevention of disease progression, by treating the underlying cause, and the alleviation of symptoms are important aims of BPH therapy. 5ARIs are the only currently available medical therapy that can reduce the risk of AUR and BPH-related surgery while providing long-term symptom control. This provides a mandate for their use in men with enlarged prostates (volume >= 30 ml), who are at increased risk of disease progression.