What are the indications, dosing regimens, contraindications, common adverse effects, and monitoring considerations for finasteride in adult males with androgenetic alopecia and benign prostatic hyperplasia?

Finasteride: Clinical Overview

Indications

Finasteride is FDA-approved for two primary indications: benign prostatic hyperplasia (BPH) at 5 mg daily and male androgenetic alopecia at 1 mg daily. 1, 2

Benign Prostatic Hyperplasia

• Finasteride is effective only in men with documented prostatic enlargement (prostate volume >30 cc); it should not be used in patients with lower urinary tract symptoms who lack gland enlargement. 1, 3
• The drug reduces prostate volume by 15-25% after 6 months of therapy, leading to an average 3-point improvement in AUA Symptom Index scores—a change patients perceive as clinically meaningful. 1, 3
• Men with larger prostates (>30-40 cc) or higher PSA values (>1.5 ng/mL) experience the greatest symptomatic and anatomical improvements. 1, 3
• Finasteride reduces the risk of acute urinary retention by 67% (from 6.3% to 4.2%) and decreases the need for BPH-related surgery by approximately 64% (from 5.4% to 2.0%). 1, 3

Male Androgenetic Alopecia

• Finasteride 1 mg daily can produce visible hair growth in up to 66% of men with mild to moderate alopecia and stops hair loss in 91% of patients. 4
• The drug is most effective when prescribed early in the course of androgenetic alopecia, before substantial hair loss has occurred. 4
• Long-term studies demonstrate sustained benefit over 5 years in placebo-controlled trials. 2

Dosing Regimens

BPH Treatment

• Standard dose: 5 mg orally once daily 1, 5, 6
• Therapy should be continued for at least 6 months before evaluating clinical response, as maximal prostate volume reduction and symptom improvement may take 6-12 months. 3, 7, 5
• Long-term studies show symptom improvements maintained for 6-10 years. 3

Androgenetic Alopecia Treatment

• Standard dose: 1 mg orally once daily 2, 4
• For men age 50 years and older, 1 mg of finasteride produces a PSA decrease similar to 5 mg (approximately 50% reduction) at 1-year follow-up. 1

Combination Therapy for BPH

• Adding finasteride 5 mg to an alpha-blocker (e.g., tamsulosin 0.4 mg) provides superior outcomes compared to monotherapy. 3, 8
• Combination therapy reduces disease progression by 67%, acute urinary retention by 79%, and need for surgery by 67% compared to alpha-blocker alone. 3, 8
• This regimen is most appropriate for men with prostate volume ≥30 cc (ideally ≥40 cc) and moderate-to-severe lower urinary tract symptoms (IPSS >8). 3, 8

Mechanism of Action

• Finasteride selectively inhibits type 2 5α-reductase, blocking conversion of testosterone to dihydrotestosterone (DHT) in the prostate, reducing DHT levels by approximately 70%. 3, 5
• The drug is well absorbed after oral administration, with peak plasma concentration reached within 1 hour, approximately 90% protein-bound, and extensively metabolized by the liver. 5

Contraindications and Precautions

Absolute Contraindications

• Women who are or may become pregnant (finasteride is pregnancy category X; DHT is essential for normal male fetal development). 5
• Hypersensitivity to finasteride or any component of the formulation. 5

Clinical Precautions

• Do not use finasteride in men with lower urinary tract symptoms who lack prostatic enlargement (<30 cc), as it is ineffective and exposes patients to unnecessary adverse effects. 1, 3
• Patients planning cataract surgery should inform their ophthalmologist if taking an alpha-blocker in combination with finasteride, due to risk of intraoperative floppy iris syndrome (IFIS) associated with alpha-blockers. 3, 8

Adverse Effects

Sexual Dysfunction (Most Common)

• Decreased libido occurs in 6.4% of patients in the first year (decreases to 2.6% in years 2-4). 1, 3
• Ejaculatory dysfunction occurs in 3.7% in the first year (decreases to 1.5% in years 2-4). 1, 3
• Erectile dysfunction occurs in 4-15% of patients. 8, 6, 9
• These sexual side effects are generally reversible and become uncommon after the first year of therapy in most patients. 1

Post-Finasteride Syndrome

• The FDA amended finasteride labels to include warnings about persistent sexual dysfunction that may continue after drug discontinuation, including erectile dysfunction, decreased libido, ejaculation disorders, and orgasm disorders. 3
• Post-finasteride syndrome (PFS) is a controversial and poorly-defined constellation of sexual, physical, and psychological symptoms that putatively persist after discontinuation; the robustness of data supporting PFS remains unclear, as it is based primarily on anecdotal patient-reported outcomes rather than prospective trials. 3

Other Adverse Effects

• Gynecomastia can occur with finasteride therapy. 1
• Hematuria is reduced with finasteride compared to placebo. 1

Prostate Cancer Considerations

• The incidence of high-grade Gleason score 8-10 prostate cancer was higher in men treated with finasteride (1.8%) compared to placebo (1.1%) in the 7-year PCPT trial. 1, 3
• However, detailed pathologic analysis suggests men taking finasteride had smaller, less aggressive tumors versus men taking placebo, with the increase in high-grade tumors more likely due to enhanced detection artifact (from reduced prostate volume improving biopsy sampling) rather than an actual increase in aggressive cancers. 1
• For men taking finasteride for BPH or male pattern baldness, the observed increase in high-grade prostate cancers and the theoretical possibility of increased prostate cancer mortality should be discussed, though reassurance can be provided that the increase is likely artifactual. 1

Monitoring Considerations

PSA Monitoring (Critical)

• Finasteride lowers PSA by approximately 50% after 12 months of therapy; therefore, a multiplier of 2 should be used when interpreting PSA values after 1 year of treatment. 1, 3, 8
• The PSA decline at 3 years may be greater than 50% (adjusted multiplier of 2.3 in the PCPT trial). 1
• Failing to adjust PSA interpretation (doubling the value after 1 year) can lead to delayed cancer diagnosis. 3
• For men age 50 years and older taking 1 mg finasteride for androgenetic alopecia, the PSA effect is similar to 5 mg (50% decrease) at 1-year follow-up. 1

Symptom Assessment

• Reassess symptoms using the International Prostate Symptom Score (IPSS) or AUA Symptom Index at 4-6 weeks and periodically thereafter. 3
• Allow a minimum of 6 months of finasteride therapy before judging treatment failure, as maximal prostate volume reduction and symptom improvement may take 6-12 months. 3, 7, 5

Post-Void Residual (PVR)

• Monitor PVR at baseline and during follow-up, especially when patients are on combination therapy or if adding antimuscarinic agents. 3, 8

Cardiovascular Considerations

• Finasteride has no direct cardiovascular effects and does not interfere with cornerstone medications for heart failure with reduced ejection fraction (HFrEF), including ACE inhibitors, ARBs, beta-blockers, mineralocorticoid receptor antagonists, or SGLT2 inhibitors. 3

Common Pitfalls to Avoid

• Do not use finasteride in patients without prostatic enlargement (<30 cc), as it is ineffective and exposes patients to unnecessary side effects. 1, 3
• Do not discontinue finasteride on the assumption that it causes nocturia; finasteride does not worsen nocturia, and its documented adverse effects are limited to sexual dysfunction. 3, 7
• Do not fail to adjust PSA values (double the measured PSA after 1 year of therapy) when screening for prostate cancer. 1, 3
• Do not evaluate treatment response before 6 months, as symptom improvement and prostate volume reduction require adequate time. 3, 7, 5
• Do not dismiss patient concerns about persistent sexual side effects, as the FDA has acknowledged these may occur despite limited prospective data. 3
• Do not assume that alpha-blocker therapy for lower urinary tract symptoms provides adequate control of co-existing hypertension; separate antihypertensive treatment may be required. 3, 8

Patient Counseling Points

• Patients should be counseled that sexual side effects typically decrease after the first year but may persist in a small subset of individuals. 3
• The disadvantages of therapy, including sexual dysfunction, should be presented against the benefits of preventing disease progression (67% reduction in acute urinary retention and BPH-related surgery). 3
• Symptom improvement from finasteride takes 3-6 months to become apparent, with maximum benefit at 6-12 months. 3
• For androgenetic alopecia, hair loss will resume following withdrawal of finasteride, confirming the drug's preservative effect. 4