What is the role of Finasteride (5-alpha-reductase inhibitor) in treating urinary obstruction caused by Benign Prostatic Hyperplasia (BPH)?

Role of Finasteride in Treating Urinary Obstruction Due to BPH

Finasteride is highly effective for treating urinary obstruction in men with BPH and enlarged prostates (≥40ml), reducing the risk of acute urinary retention by 67% and the need for BPH-related surgery by 64% compared to placebo. 1

Mechanism and Efficacy

Finasteride is a 5-alpha-reductase inhibitor (5-ARI) that works by:

• Inhibiting the conversion of testosterone to dihydrotestosterone (DHT)
• Reducing prostate volume by 20-30% after 6-12 months of therapy 2
• Improving urinary symptoms and increasing urinary flow rates 1

The medication demonstrates several important clinical benefits:

• Reduces the risk of acute urinary retention by 57-67% 1, 3
• Decreases the need for surgical intervention by 55-64% 1, 3
• Provides sustained improvement in urinary symptoms over long-term use 3

Patient Selection

Finasteride is most appropriate for:

• Men with moderate-to-severe LUTS and enlarged prostates (≥40ml) 2
• Patients at risk for disease progression 2
• Those seeking to avoid surgery or acute urinary retention 1

It is less effective in men with small prostates (<40ml), where alpha-blockers may be preferred 2, 4.

Treatment Regimen

• Standard dosage: 5mg once daily for BPH 2, 1
• Maximum efficacy typically achieved after 12 months of continuous therapy 2
• Long-term therapy is necessary as withdrawal results in prostate regrowth 5

Combination Therapy

Combination therapy with alpha-blockers provides additional benefits:

• Finasteride plus an alpha-blocker (e.g., doxazosin) is the most effective medical therapy for men with moderate-to-severe LUTS and enlarged prostates 2
• Combination therapy reduces the risk of symptomatic progression more effectively than either agent alone 1
• In the MTOPS study, combination therapy reduced symptom progression by 64% compared to placebo, which was superior to finasteride alone (30% reduction) 1

Monitoring and Follow-up

• Initial assessment of response after 4-12 weeks of treatment 2
• Full efficacy assessment after 6-12 months of therapy 5
• PSA values should be doubled for prostate cancer screening in patients on finasteride (as it reduces PSA by approximately 50%) 2
• Regular monitoring of post-void residual volume is recommended 2

Adverse Effects

Common side effects include:

• Sexual dysfunction (decreased libido, erectile dysfunction, ejaculation disorders) in approximately 2-3% of patients 2, 5
• Gynecomastia (reported in 0.4% of patients) 6

These adverse effects are generally mild and rarely lead to treatment discontinuation.

Common Pitfalls to Avoid

1. Prescribing finasteride for small prostates where efficacy is limited 2
2. Expecting rapid symptom improvement (full benefits may take 6-12 months) 2, 5
3. Discontinuing therapy too early before maximum benefits are achieved 2
4. Not adjusting PSA values for prostate cancer screening 2
5. Using finasteride alone when combination therapy with an alpha-blocker would be more effective for symptomatic relief 4

Clinical Decision Algorithm

1. For men with moderate-to-severe LUTS and enlarged prostates (≥40ml):

   • First-line: Combination therapy with finasteride and alpha-blocker
   • Alternative: Finasteride monotherapy if alpha-blockers are contraindicated

2. For men with moderate-to-severe LUTS and small prostates (<40ml):

   • First-line: Alpha-blocker monotherapy
   • Alternative: Tadalafil 5mg daily (especially with concomitant erectile dysfunction)

3. For men with mild-moderate symptoms and risk factors for progression:

   • Consider finasteride to prevent disease progression

4. For men awaiting surgery or at high risk for acute urinary retention:

   • Finasteride is strongly recommended to reduce these risks