What is the effectiveness of finasteride (5-alpha-reductase inhibitor) for Benign Prostatic Hyperplasia (BPH)?

Effectiveness of Finasteride for Benign Prostatic Hyperplasia (BPH)

Finasteride is an effective treatment for BPH that reduces prostate size by 15-25%, improves urinary symptoms by an average of 3-4 points on symptom scores, and significantly reduces the risk of BPH progression including acute urinary retention (by 67%) and need for surgery (by 64%) compared to placebo. 1, 2

Mechanism of Action and Effects

• Finasteride inhibits 5-alpha-reductase type II isoenzyme, reducing dihydrotestosterone (DHT) in the prostate by approximately 70%, leading to a 15-25% reduction in prostate size within 6 months 1
• This reduction in prostate size results in improved peak urinary flow rates and reduced BPH symptoms 1
• Finasteride decreases serum PSA levels by approximately 50%, which must be considered when screening for prostate cancer 1, 3

Clinical Efficacy

• Patients experience an average 3-point improvement in symptom scores, which is generally perceived as a clinically meaningful change 1, 3
• Long-term studies demonstrate that symptom improvements of 3-4 points are maintained for 6-10 years with continued finasteride therapy 1, 3
• In the MTOPS study, finasteride reduced the risk of BPH progression by 34% compared to placebo 2
• Finasteride significantly reduces the risk of acute urinary retention by 67% and the need for BPH-related surgery by 64% compared to placebo 2
• The medication is particularly effective in men with larger prostates (>30cc) and/or higher PSA values 1, 3

Patient Selection

• Finasteride is most appropriate for patients with lower urinary tract symptoms (LUTS) who have evidence of prostatic enlargement, defined as a prostate volume greater than 30cc on imaging 1, 3
• The medication is ineffective in patients without prostatic enlargement and should not be prescribed for these individuals 1, 3
• Finasteride is FDA-approved for:
  • Improving symptoms of BPH
  • Reducing the risk of acute urinary retention
  • Reducing the risk of BPH-related surgery 2

Comparison to Other Treatments

• Finasteride is less effective than alpha blockers (such as doxazosin and terazosin) for immediate symptom relief 1, 4
• However, finasteride provides long-term benefits in reducing disease progression that alpha blockers do not 1, 2
• Combination therapy with finasteride and an alpha blocker (such as doxazosin) is more effective than either medication alone, reducing the risk of BPH progression by 67% compared to placebo 2
• Combination therapy is particularly beneficial for patients with very large prostates or severe symptoms 1, 4

Side Effects and Considerations

• Common side effects include:
  • Decreased libido (6.4% in first year, 2.6% in years 2-4) 1
  • Ejaculatory dysfunction (3.7% in first year, 1.5% in years 2-4) 1
  • Erectile dysfunction 4
• These sexual side effects are typically reversible and become less common after the first year of therapy 1, 5
• Finasteride has a slower onset of action compared to alpha blockers; patients should be counseled that symptom improvement may take several months 1

Treatment Algorithm

1. Confirm prostatic enlargement (>30cc) before initiating finasteride 1, 3
2. For patients with moderate symptoms and documented prostate enlargement:
   • Start with finasteride 5 mg daily 6
   • Continue therapy for at least 6 months before evaluating clinical response 6
3. For patients needing more immediate symptom relief:
   • Consider combination therapy with finasteride and an alpha blocker 1, 2
4. For patients with severe symptoms or acute urinary retention:
   • Consider surgical options like TURP if medical therapy fails 3

Common Pitfalls to Avoid

• Using finasteride in patients without prostatic enlargement (<30cc) is ineffective 1, 3
• Inadequate treatment duration - finasteride requires at least 6 months for full effect 1, 6
• Failure to adjust PSA interpretation - PSA levels decrease by approximately 50% after 12 months of therapy, so measured PSA should be doubled when screening for prostate cancer 1, 3
• Not considering combination therapy with an alpha blocker for patients with severe symptoms or very large prostates 1, 3, 2