The effect of finasteride on the risk of acute urinary retention and the need for surgical treatment among men with benign prostatic hyperplasia 

Authors McConnell M, Bruskewitz R, Walsh P, Andriole G, Lieber M, Holtgrewe H, Waldstreicher J, et al for the Finasteride Long-Term Efficacy and Safety Study Group 
Source New England Journal of Medicine. 338:557-63. February 26, 1998. 
Institutions Multiple university hospitals in the United States, Queen's University, Canada and Merck Research Laboratories. 
Support Merck 


Finasteride decreases the conversion of testosterone to dihydrotestosterone and can reduce the volume of the prostate in men with prostatic hypertrophy. This study was designed to look at the efficacy of finasteride in improving symptoms and reducing the incidence of urinary retention and prostate surgery in men with symptomatic, enlarged prostate glands.



Patients were enrolled between 1990 and 1992. 

Inclusion criteria: Moderate to severe obstructive symptoms (by a questionnaire), decreased urinary flow rate (<15 ml/sec), enlarged prostate gland on digital rectal examination and serum PSA < 10 ng/ml. 

Men with a serum PSA between 4.0 and 9.9 were required to have a negative biopsy for cancer. 

Exclusion criteria: Use of alpha-blockers, anti-androgens, chronic prostatitis, prostate or bladder cancer or surgery. 


Patients were randomized to finasteride, 5 mg, or placebo daily. Follow-up was every four months for symptoms and measurement of urinary flow rates. PSA measurements, physical examinations including digital rectal exams and routine bloodwork were performed at regular intervals. Prostate volume was measured by MRI yearly in a subset of patients. 

Overall follow-up was for four years. At the end of the study, it was requested that patients who had undergone a prostate biopsy at baseline (PSA > 4.0) undergo another biopsy. 


The primary endpoint was the change in a symptom score determined by self-administered questionnaire and subsequently converted to a "quasi-AUA score" (the AUA score was adopted after this study was designed). 

Predetermined secondary endpoints were the occurence of acute urinary retention (classified as spontaneous or precipitated) and surgery for benign prostatic hypertrophy. 



3040 patients were enrolled. Baseline characteristics were similar in the two groups. Overall age was 64 years; 95% of patients were white. The baseline quasi-AUA score was 15; urinary flow rate 11 ml/min; prostate volume was 55 ml (measured in 312 men); serum PSA was 2.8 ng/ml. 

Discontinuation of drug
  Finasteride (1524) Placebo (1516)
Withdrawals due to:    
Adverse events 176 166
Lack of improvement or worsening of disease 122 160
Need for surgery or medical therapy 80 172
Other reasons or lost to f/u 146 135
Total withdrawals 524 633
Completed 4 years of study 1000 883
Complete outcomes data until study end or withdrawal available 1384 (91%) 1376 (91%)

Symptom score

The symptom score (converted to the quasi-AUA score) decreased by 2.6 points in the finasteride group and by 1.0 in the placebo group (p<0.001). Among men who completed the study, the corresponding decreases were 3.3 and 1.3). Symptom scores decreased by about the same amount in both groups during the first 8 months, then continued to decrease in the finasteride group but levelled off in the placebo group. 

Surgery and acute urinary retention

Prostate surgery (predominantly TURP) was performed in 10% of men in the placebo group and in 5% in the finasteride group (p<0.001). 

Acute urinary retention (about one half spontaneous and one half precipitated) occurred in 7% of men in the placebo group and in 3% in the finasteride group (p<0.001). 

The curves for surgery and urinary retention diverged between the two groups constantly over time. 

Other results

  • Mean prostate volume increased steadily over time in the placebo group, to about +14% after 4 years. In the finasteride group there was an initial drop after one year (about -18%) which remained constant thereafter. 

  • Urinary flow rate remained about the same in the placebo group, and increased gradually to +1.9 ml/min in the finasteride group. 

  • There was an increased incidence of sexual dysfunction in the finasteride group during the first year: decreased libido 6.4% vs. 3.4% and impotence  8.1% vs. 3.7%. These differences did not persist after the first year [possibly related to withdrawals from the study?]. 

  • Prostate cancer cancer occurred in 5% of men in both groups. 


    Author's discussion

    The authors state that the most important result of this trial is the reduction in the need for prostate surgery and in the incidence of acute urinary retention in the finasteride group. Although alpha-adrenergic blocking drugs have been shown to decrease symptoms, they have not been shown to decrease the need for surgery or the incidence of urinary retention (which carries its own morbidity and increases the incidence of surgery). 

    They note that this trial was limited to men with clinically enlarged prostate glands and moderate to severe symptoms, and that the results may not apply to men who do not fulfill these criteria. 



    This was a 4-year randomized study of finasteride vs. placebo in men with moderate to severe symptoms of obstructive uropathy and clinically enlarged prostate glands. It demonstrated a significant improvement in symptoms, as well as a significant decrease in the need for surgery (5% vs. 10%) and the incidence of acute urinary retention (3% vs. 7%) over 4 years in the finasteride group. This translates into a Number Needed to Treat of 20 patients treated for 4 years to prevent one prostate operation. 

    Only men with enlarged prostates on rectal examination and moderate to severe symptoms were included in this study. This is important to note, since previous studies of finasteride vs. alpha-blockers for symptoms of obstructive uropathy indicate that finasteride's effect may be limited to men with enlarged prostate glands. A study published in the NEJM in 1996, which did not require evidence of prostatic enlargement on physical exam, found no benefit for finasteride, but a significant benefit of terazosin. In an editorial published along with that study, Walsh hypothesizes that obstructive symptoms may be due to smooth muscle hyperplasia or to glandular hyperplasia. Men with smaller prostates and obstructive symptoms are more likely to suffer from smooth muscle hyperplasia and would not be expected to benefit from finasteride but would benefit from an alpha blocker. Men with large prostates are more likely to have glandular hyperplasia, which would be expected to respond to an anti-testosterone agent such as finasteride. Thus, the results presented here cannot be automatically extrapolated to all men with obstructive uropathy symptoms, only to those with clinically enlarged prostates. 

    One point not addressed in the article is the serum PSA level. In this study, men with mildly elevated PSA levels were required to undergo a prostate biopsy in order to participate in the study. This probably caused a bias towards lower PSA levels among study patients, since many patients with only mildly elevated PSA levels would be reluctant to undergo this procedure. In fact, despite the fact that the average prostate volume was elevated (55 ml), the average serum PSA was only 2.8 ng/ml. This could conceivably have biased the results, possibly against finasteride, since an elevated PSA level could be a marker for glandular tissue responsive to the drug. It would have been instructive to know the effect of serum PSA levels on the study results. 

    It is interesting that the primary endpoint of this study was the improvement in symptoms with finasteride, whereas the most important results were represented by the secondary endpoints (surgery and urinary retention). At the time the study was initiated, it was already known that finasteride significantly improved symptoms in men with enlarged prostate glands. Thus, the choice of primary endpoint was presumably made to ensure a positive result of the trial, while leaving open the possibility of emphasizing the importance of the secondary endpoints if they turned out to be significant, as was the case. Although this is not a major problem, the primary endpoints of a study are those upon which sample size determinations are usually made, and should represent the main topic being studied. 

    March 9, 1998 


    References related to this article from the NLM's PubMed database. 

    Reader Comments

    Date: Fri, 20 Mar 98

     The article posted was very interesting. I have even found finasteride produced some symptomatic improvement in what turned out to be a definite carcinoma. I don't think its use should mask the diagnosis as I usually, as a general practitioner, take a PSA before starting treatment. I also usually refer to a urologist for biopsy etc. In my experience finasteride is well tolerated.

    John Warre. (UK) 

      The problem of finasteride potentially masking symptoms of prostate cancer (and thus delaying diagnosis) would also apply to alpha-blockers. The importance of evaluating urinary obstructive symptoms for potential prostate cancer should be borne in mind. --mj 


    Thu, 26 Mar 1998
    From: sachin dave <>

    I have two comments:

    How sensitive is digital prostatic examination (DPE) to identify an enlarged prostate gland? Are there any studies available? If not, then the decision to include patients in the study should have been based on objectively (sonogram/MRI) documented gland size enlargement instead of DPE i.e. any patient with symptoms of prostatism should have been subjected to these exams before inclusion in the study. Because we often encounter patients with normal prostate size (muscular component predominence hypothetically) who may have an enlarged prostate missed by DPE. That would have helped in assesing sensitivity and specificity of DPE as well, considering Sonogram/MRI as gold standard.

    How long does it take for finasteride to become effective once we start it on a patient with Benign Prostatic Hypertrophy (BPH) ( given the hypothesis that it decreases glandular component of Prostate)? What should be done for patients with symptoms of prostatism meanwhile? Use alphablockers? We may have to reconsider our options. Is finasteride overrated for BPH? I am glad it has found another medical use [for baldness. mj]. 

      This study (together with others) suggests that finasteride is more likely to be efficacious in patients with an enlarged prostate and obstructive symptoms than in patients whose gland is not enlarged. It is true that gland size can be more accurately assessed using imaging techniques than by digital examination alone, and many patients will end up undergoing imaging for the purpose of cancer screening, but it does not seem reasonable to require every patient with obstructive symptoms to undergo imaging solely to decide on the appropriateness of finasteride therapy. This study was designed to look at the utility of finasteride in patients with clinically enlarged glands, without requiring confirmatory imaging (although many patients did, in fact, undergo MRI).

      Alpha blockers are likely to be effective more rapidly than finasteride, and may need to be given initially along with finasteride if rapid symptomatic improvement is desired. --mj 

    Mon, 22 Feb 1999
    From: Amit Ghosh <>

    Evidence based medicine uses the term number needed to treat (NNT) very often to discuss the clinical significance of a therapy. It is defined as the number of patients needed to be treated in order to obtain one benefit. NNT is calculated as 100 / (absolute risk reduction). In the Study by McConnell et. al the absolute risk reduction due to the use of finasteride was 7%-4%= 3%, and the NNT is 100/3=33. Despite the statistical significance, one needs to treat 33 patients with finasteride to get 1 fewer episode of urinary retention.  The NNT for prostate surgery was 20, which seemed to be clinically more relevant information. The NNH (number needed to harm) was about 23 for impotence during the first year of treatment. One needs to use these numbers when discussing the risks versus benefit of finasteride therapy with patients. Both groups were equally affected by prostate cancer.

    Amit Ghosh, MD
    University of Minnesota
    Minneapolis, MN 55455

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