What is the recommended dosing for finasteride (Propecia) in the treatment of benign prostatic hyperplasia (BPH) and androgenetic alopecia?

Finasteride Dosing

For benign prostatic hyperplasia (BPH), finasteride is dosed at 5 mg once daily, while for androgenetic alopecia (male pattern hair loss), the dose is 1 mg once daily. 1

Dosing for Benign Prostatic Hyperplasia (BPH)

Standard Dose

• Finasteride 5 mg once daily is the recommended dose for BPH treatment 1
• The medication can be taken with or without food, as bioavailability is not affected by food intake 1

Patient Selection Criteria

• Finasteride is appropriate only for patients with documented prostatic enlargement (prostate volume >30cc on imaging) 2
• Do not use finasteride in men with lower urinary tract symptoms (LUTS) who lack prostatic enlargement, as it will be ineffective 2

Timeline for Response

• Maximum DHT suppression occurs approximately 8 hours after the first dose and is maintained throughout the 24-hour dosing interval 1
• Prostate volume decreases by approximately 15-25% within 6 months of treatment 2
• Patients should be counseled that symptom improvement may take 3-6 months, as finasteride has a slower onset of action compared to alpha-blockers 2
• A therapeutic trial of at least 6 months is generally necessary to assess whether a beneficial response has been achieved 1

Combination Therapy Considerations

• For patients with moderate-to-severe LUTS (AUA Symptom Score >8) and prostatic enlargement (>30cc), combination therapy with an alpha-blocker is more effective than finasteride monotherapy 2
• Combination therapy reduces the risk of overall BPH clinical progression by 67% compared to 39% for alpha-blockers alone and 34% for 5α-reductase inhibitors alone 3

Dosing for Androgenetic Alopecia (Male Pattern Hair Loss)

Standard Dose

• Finasteride 1 mg once daily is the approved dose for treating male pattern hair loss 4, 5
• This lower dose effectively inhibits 5α-reductase, preventing conversion of testosterone to dihydrotestosterone (DHT) in scalp tissue 4

Duration of Treatment

• Long-term use (up to 5 years) has been studied in placebo-controlled trials with demonstrated efficacy and safety 5
• Treatment must be continued to maintain hair growth benefits, as discontinuation results in reversal of improvements 1

Critical Monitoring Considerations

PSA Adjustment

• Finasteride 5 mg/day decreases serum PSA levels by approximately 50% after 12 months of therapy 2, 1
• When screening for prostate cancer in men on finasteride 5 mg, the measured PSA value should be doubled after 1 year of therapy 2
• Finasteride 1 mg/day for androgenetic alopecia also significantly lowers PSA: by 40% in men aged 40-49 years and 50% in men aged 50-60 years within 48 weeks 6
• The existing recommendation for PSA adjustment in men taking 5 mg/day should also apply to men taking 1 mg/day for hair loss 6

Pharmacokinetics

• Mean elimination half-life is approximately 6 hours (range 3-16 hours) 1
• Steady-state concentrations are achieved with slow accumulation after multiple dosing 1
• After discontinuation, DHT levels return to pretreatment levels in approximately 2 weeks 1
• Prostate volume returns to near baseline approximately 3 months after discontinuation 1

Common Adverse Effects

Sexual Side Effects (5 mg dose for BPH)

• Decreased libido occurs in 6.4% of patients in the first year, declining to 2.6% in years 2-4 2
• Ejaculatory dysfunction occurs in 3.7% of patients in the first year, declining to 1.5% in years 2-4 2
• Impotence was reported in 8.1% of finasteride-treated patients versus 3.7% of placebo patients in year 1 1
• These side effects are typically reversible and become less common after the first year of therapy 2

Sexual Side Effects (1 mg dose for alopecia)

• Most studies found that finasteride 1 mg for androgenetic alopecia was not correlated with erectile dysfunction 7
• The most common adverse events at the 1 mg dose include reduced libido, decreased ejaculate volume, and gynecomastia 4

Key Clinical Pitfalls to Avoid

• Do not use finasteride in patients without documented prostatic enlargement (>30cc), as it is ineffective and exposes patients to unnecessary side effects 2, 3
• Do not discontinue therapy prematurely due to lack of immediate symptom relief; allow at least 6 months to assess efficacy 2, 1
• Always adjust PSA interpretation by doubling the measured value after 12 months of therapy to avoid missing prostate cancer 2
• Do not confuse the dosing: 5 mg daily for BPH versus 1 mg daily for alopecia 1, 4

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