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Prostate volume predicts BPH outcome with finasteride

More on BPH

Treatment of benign prostatic hypertrophy has been further informed by a meta-analysis and a large randomised controlled trial (RCT). The meta-analysis looked at results after one year on finasteride or placebo, and the RCT examined effects after two years of treatment. Bandolier has a quibble with both of these reports. Each has lovely statistics and large numbers, but both lack a clear statement of what constitutes clinical improvement in men with BPH, either in terms of peak urine flow rate, or in terms of symptom scores. And without that, and with just means, no NNTs can be calculated from the published data, which is disappointing considering the quality of the studies.


This examined one-year results of six RCTs comparing finasteride and placebo [1]. There were 2601 men randomised between finasteride 5 mg or placebo daily for one year. Prostate volume was measured by trans-rectal ultrasound (TRUS) or MRI.

The bottom line was that finasteride is only effective in men with prostate volumes of more than 40 mL. The Figure shows data from a single patient analysis for peak urine flow rate, though a similar picture emerges for symptom scoring. The conclusion was that men with small prostates may not be suitable candidates for finasteride therapy.

RCT - two year outcomes

The RCT enrolled 707 men with moderate symptoms of BPH and treated them with 5 mg finasteride or placebo daily for two years.

The main results were that men on placebo had worsening symptom scores and urine flow rates in the second year of treatment, whereas men on finasteride maintained the benefits seen in the first year of treatment. There was sufficient information to calculate some NNT values (Table). For instance, prostate volumes increased in 56% of men on placebo, but only 16% of men on finasteride. The NNT of 2.5 indicates that finasteride has to be given to five men for two years to prevent an increase in prostate volume of more than 1 mL in two, in whom this would not have been prevented with placebo.

Finasteride versus placebo for BPH: two-year outcomes
Outcome NNT (95%CI)
Prevent prostate volume increase of more than 1 mL 2.5 (2.1 to 3.2)
Prevent one patient developing urinary retention 32 (18 to 136)
Prevent one patient having prostate surgery 39 (23 to 111)
Prevent one patient discontinuing because of insufficient response 39 (17 to no difference)
Cause one case of sexual dysfunction 11 (6.9 to 23)
One patient in 30 to 40 would stop the drug because of insufficient response, or because of urinary retention or surgery. For finasteride to cause one case of sexual dysfunction had an NNT of 11.


The accumulating information on finasteride treatment of BPH is giving more clear indications on which men can benefit (those with prostate volumes >40 mL) and that the benefits seen in one-year studies continue at least to two years. The lack of information to calculate NNTs for clinically relevant outcomes (and what they might be) still eludes us.


  1. P Boyle, AL Gould, CG Roeherborn. Prostate volume predicts outcome of treatment of benign prostatic hyperplasia with finasteride: meta-analysis of randomized clinical trials. Urology 1996 48: 398-405.
  2. JT Andersen, P Ekman, H Wolf et al. Can finasteride reverse the progress of benign prostatic hyperplasia? A two-year placebo-controlled study. Urology 1995 46: 631-7.

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