Two separate phase III clinical trials studying symptomatic patients with palpably enlarged prostates were conducted to evaluate the safety and efficacy of finasteride in treating symptomatic BPH. These 12-mo studies of men receiving either 5 mg of finasteride or placebo daily were performed in a randomized, double-blind, placebo-controlled fashion. In the first trial, the North American Study, men who received finasteride 5 mg/d (n = 297 patients) had a decrease in prostate volume of 19% vs a 3% drop noted in men taking placebo (n = 300 patients) (25). In the International Study, also known as the Finasteride Study Group, men receiving 5 mg/d of finasteride experienced a 22% drop in prostate volume, compared to a 5% drop in the placebo group (26). Regarding maximum urinary flow rate, men in the North American Study group treated with 5 mg/d of finasteride had a statistically significant but clinically limited increase in maximum flow rate of 1.6 mL/s; men receiving placebo were found to have a gain of only 0.2 mL/s. Similar results of 3.7 mL/s mean difference in maximum urinary flow rate with finasteride 5 mg/day compared with placebo were observed after initiation of treatment in the International Study. A significant but limited improvement in urinary symptoms on a modified Boyarsky questionnaire accompanied these changes (24-26).
In both phase III trials, adverse side effects associated with finasteride were evaluated. On the basis of these studies, finasteride was shown to be clinically safe. The incidence of adverse side effects for finasteride patients in both studies was limited and was generally quite similar to the incidence in placebo patients. Exceptions to this included a higher incidence of decreased libido, erectile dysfunction, and diminished ejaculate volume in patients receiving finasteride.
The phase III trials were extended in an open-label fashion for up to 7 yr. No increase in adverse events was noted over the course of the open-label component, and the total incidence of study drop-outs as a result of sexual adverse events was 2-3 % over the 5- to 7-yr extension period (27,28). More importantly, the decrease in prostate volume seen at the end of the first 12 mo of treatment was maintained throughout the next 5 yr of open-label study, and gains in urinary flow rate and symptom score were maintained and even increased during the 4-yr extension. The issue of patient selection for these open-label studies is obviously a possible confounding variable. However, the results sug gested that long-term use of finasteride effectively sustained the limited gains seen after 12 mo in prostate volume, urinary flow rate, and symptom score, with an excellent safety and tolerability profile.
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