A risk-benefit assessment of treatment with finasteride in benign prostatic hyperplasia

As an androgen target organ, the prostate gland has the almost unique characteristic of being less sensitive to testosterone than to its metabolite 5 alpha-dihydrotestosterone (5 alpha-DHT). The conversion of testosterone to 5 alpha-DHT is induced by the enzyme 5 alpha-reductase. By blocking the activity of 5 alpha-reductase, the androgenic stimulation of the prostate gland can be significantly reduced. The first drug with such capacity to be introduced on the market was finasteride. Following the administration of this drug to men, serum 5 alpha-DHT levels were reduced by approximately 80%. Large phase III trials have demonstrated the efficacy of finasteride in treating benign prostatic hyperplasia (BPH). While in some patients the drug was poorly effective, other patients showed significant improvements. The mean reduction in size of the prostate gland was 20 to 25% after 6 months of therapy, and this effect was maintained as long as the patient was on the drug, at least up to the end of a 6-year follow-up period. Prostatic symptom scores were improved by a mean of 30%, while urinary flow was only improved by a mean of 1.5 ml/sec (15%). In a recent double-blind, placebo-controlled study comparing the alpha-blocker terazosin with finasteride, significant improvement was demonstrated for the alpha-blocker, while finasteride produced little improvement overall and was not significantly more effective than placebo in treating moderately symptomatic BPH. However, a subanalysis of this study showed that while finasteride was poorly effective in patients with small prostate glands, a significant improvement was apparent in those with glands larger than 40ml. There is some evidence that early intervention with finasteride can reduce the number of surgical procedures that are required, at least over a 2-year period. Finasteride is very well tolerated. However, since 5 alpha-DHT potentiates erectile capacity, a 3 to 4% incidence of impotence has been reported, as well as a decreased ejaculatory volume. Gynaecomastia has been noted in a few patients (0.4%). In conclusion, finasteride appears to be a very well tolerated drug to treat outflow obstruction in patients with moderately symptomatic BPH caused by large prostate glands.