BPH Medications: 5-Alpha Reductase Inhibitors (Finasteride, Dutasteride)

What are 5-alpha reductase inhibitors (5-ARIs)?

5-alpha reductase inhibitors (5-ARIs) are medications that block the enzyme 5-alpha reductase, which converts testosterone into dihydrotestosterone (DHT). DHT is the primary hormone that stimulates prostate growth.

By lowering DHT levels in the prostate, 5-ARIs shrink the prostate gland – addressing the "static" component of BPH obstruction.

How do 5-ARIs help BPH?

BPH is driven by DHT (dihydrotestosterone). 5-ARIs:

• Reduce intraprostatic DHT levels by 80-95%
• Induce apoptosis (programmed cell death) in prostate epithelial cells
• Shrink the prostate by 20-30% (volume reduction)
• Improve urine flow and reduce symptoms
• Reduce the risk of acute urinary retention and need for BPH surgery

Finasteride (Proscar) – the original 5-ARI

Finasteride was the first 5-ARI approved for BPH (1992). It is also used at a lower dose (1 mg) for male pattern baldness (Propecia).

• Dosing for BPH: 5 mg once daily
• Type: Inhibits type 2 5-alpha reductase (not type 1)
• Prostate size reduction: 20-25% over 6-12 months
• IPSS improvement: 15-25% reduction
• Peak flow (Qmax) improvement: 1.5-2.0 mL/s increase
• Onset of action: 3-6 months (slow)
• Side effects: ED (4-6%), decreased libido (3-5%), ejaculatory dysfunction (1-2%)

Dutasteride (Avodart) – dual inhibitor

Dutasteride is a newer 5-ARI that inhibits both type 1 and type 2 5-alpha reductase enzymes.

• Dosing for BPH: 0.5 mg once daily
• Type: Dual inhibitor (types 1 and 2)
• Prostate size reduction: 25-30% over 6-12 months (slightly more than finasteride)
• IPSS improvement: Similar to finasteride (15-25%)
• Peak flow (Qmax) improvement: 1.5-2.5 mL/s increase
• Onset of action: 3-6 months (similar to finasteride)
• Side effects: ED (5-7%), decreased libido (4-6%), ejaculatory dysfunction (2-3%)
• Half-life: 5 weeks (longer than finasteride's 6-8 hours)

Finasteride vs. Dutasteride – key differences

• Enzyme inhibition: Finasteride blocks only type 2; dutasteride blocks both type 1 and type 2.
• DHT reduction: Finasteride reduces serum DHT by 70-80%; dutasteride reduces by 90-95%.
• Prostate shrinkage: Dutasteride causes slightly more shrinkage (25-30% vs. 20-25%).
• Half-life: Dutasteride has a much longer half-life (5 weeks vs. 6-8 hours).
• Effectiveness: Most studies show similar clinical efficacy; dutasteride may be marginally better.
• Side effects: Similar rates; dutasteride may have slightly higher sexual side effects.
• Cost: Finasteride is generally less expensive (generic available).

Effectiveness – symptom improvement, flow rate, prostate size reduction

Clinical trial data (4-year studies):

• IPSS reduction: 15-25% improvement (e.g., from 18 to 14-15)
• Peak flow (Qmax) increase: 1.5-2.5 mL/s
• Prostate volume reduction: 20-30% (maximum at 6-12 months)
• Risk reduction for acute urinary retention: 50-60%
• Risk reduction for BPH surgery: 50-60%

5-ARIs are most effective in men with larger prostates (>40 mL). Men with small prostates (<30 mL) derive little benefit.

Side effects – ED, decreased libido, ejaculation disorders, gynecomastia

Sexual side effects are the most common reason for discontinuing 5-ARIs:

• Erectile dysfunction (ED): 4-7% (finasteride) vs. 5-8% (dutasteride) – higher than placebo (2-3%)
• Decreased libido (reduced sex drive): 3-6%
• Ejaculatory dysfunction: Reduced ejaculate volume (1-2%) – less common than with alpha-blockers
• Gynecomastia (breast enlargement/tenderness): 1-2% – due to increased estrogen/testosterone ratio
• Rare side effects: Depression, anxiety, post-finasteride syndrome (very rare, controversial)

Post-Finasteride Syndrome (PFS):

A small number of men report persistent sexual, neurological, and physical side effects after stopping finasteride. This is rare and controversial; most men have no long-term issues.

PSA effects – why PSA drops by ~50%

5-ARIs significantly lower PSA levels – an important consideration for prostate cancer screening:

• PSA reduction: Finasteride lowers PSA by ~50% after 6-12 months; dutasteride lowers by ~50-60%.
• Clinical guideline: If a man is on a 5-ARI, his PSA should be doubled for comparison to normal ranges (e.g., a PSA of 1.5 ng/mL on finasteride would be equivalent to 3.0 ng/mL off the drug).
• Baseline PSA: Establish a baseline PSA before starting 5-ARIs. After 6 months, a new baseline is established (about half the original).
• Rising PSA on 5-ARI: Any confirmed rise in PSA while on a 5-ARI is concerning for prostate cancer and requires evaluation.

Combination therapy with alpha-blockers

Combining a 5-ARI with an alpha-blocker is superior to either alone for men with larger prostates (>40 mL):

• Rapid relief: Alpha-blocker provides symptom improvement in days
• Long-term benefits: 5-ARI shrinks the prostate and reduces complications
• MTOPS study (Medical Therapy of Prostatic Symptoms): Combination therapy reduced risk of BPH progression by 66% compared to placebo and 40% compared to alpha-blocker alone.
• When to start: For men with IPSS ≥8, prostate size >40 mL, and bothersome symptoms.

Who should take 5-ARIs? (Prostate size >40 mL)

5-ARIs are NOT for every man with BPH. Ideal candidates:

• Prostate size >40 mL (measured by ultrasound or DRE estimation)
• Moderate to severe symptoms (IPSS ≥8)
• Willing to wait 3-6 months for maximum effect
• Desire to reduce risk of BPH progression (acute retention, surgery)
• Not planning to father children (5-ARIs can affect sperm parameters – reversible)

Men with small prostates (<30 mL) derive little benefit from 5-ARIs and should use alpha-blockers or other treatments.

Time to effect – slow onset (3-6 months)

Unlike alpha-blockers (days), 5-ARIs work slowly:

• Week 1-4: No noticeable effect
• Month 3: Some symptom improvement begins
• Month 6: Maximum symptom improvement (IPSS reduction 15-25%)
• Month 12: Maximum prostate shrinkage (20-30%)

If no improvement by 6-9 months, consider alternative therapy.

Comparison table – 5-ARIs vs. alpha-blockers

Interactive FAQ – 5-alpha reductase inhibitors for BPH

Disclaimer: This information is for educational purposes. 5-alpha reductase inhibitors are prescription medications. Discuss risks and benefits with a urologist at Vivekananda Hospital before starting treatment.