finasteride (Rx)

1-10%

Erectile dysfunction (1.3-8.1%)

Decrease libido (1.8-6.4%)

Breast enlargement (0.5-1.8%)

Ejaculation disorder (0.8-1.2%)

<1%

Breast tenderness (0.4-0.7%)

Rash (0.5%)

Postmarketing Reports

Neoplasms: Male breast cancer

Breast disorders: Breast tenderness and enlargement

Nervous system/psychiatric: Depression

Hypersensitivity reactions: Rash, pruritus, urticaria, and angioedema (including swelling of the lips, tongue, throat, and face)

Reproductive system: Sexual dysfunction that continued after discontinuation of treatment, including erectile dysfunction, libido disorders, ejaculation disorders, and orgasm disorders; male infertility and/or poor seminal quality (normalization or improvement of seminal quality has been reported after discontinuation of finasteride); testicular pain

Contraindications

Hypersensitivity

Women of childbearing potential

Cautions

Use with caution with obstructive uropathy; carefully monitor patients with large residual urinary volume or severely diminished urinary flow

Use caution in liver disease

May cause decreased serum PSA in presence of prostate cancer; increases in PSA levels from nadir while on finasteride may signal the presence of prostate cancer and should be carefully evaluated (even if PSA value within normal range)

Pregnant and potentially pregnant women should not handle crushed or broken tablets or semen of male partner; may have negative impact in fetal development

Rare reports of male breast cancer observed with use; any breast tenderness, enlargement, pain, lumps, nipple discharge or any other type of breast changes should be reported immediately to healthcare provider

5-ARIs and prostate cancer risk

• June 9, 2011: Recent data from 2 large, randomized, controlled trials observed a reduction in overall incidence of prostate cancer but an increased risk of being diagnosed with a more serious form of prostate cancer (high-grade prostate cancer) in trial participants taking 5-alpha reductase inhibitors (5-ARIs)
• The 2 trials are the Prostate Cancer Prevention Trial (PCPT) and the Reduction by Dutasteride of Prostate Cancer Events (REDUCE) trial
• The revised prescribing information recommends that prior to initiating therapy with 5-ARIs, appropriate evaluation should be performed to rule out other urologic conditions, including prostate cancer, that might mimic benign prostatic hyperplasia (BPH)
• A minimum of 6 months may be necessary to assess response in BPH

Pregnancy category: X

Lactation: Excretion in milk unknown; contraindicated

Pregnancy Categories

A: Generally acceptable. Controlled studies in pregnant women show no evidence of fetal risk.

B: May be acceptable. Either animal studies show no risk but human studies not available or animal studies showed minor risks and human studies done and showed no risk.

C: Use with caution if benefits outweigh risks. Animal studies show risk and human studies not available or neither animal nor human studies done.

D: Use in LIFE-THREATENING emergencies when no safer drug available. Positive evidence of human fetal risk.

X: Do not use in pregnancy. Risks involved outweigh potential benefits. Safer alternatives exist.

NA: Information not available.

Mechanism of Action

Selective inhibitor of type 1 & type 2 isoforms of 5-alpha-reductase; suppresses serum dihydrotestosterone levels by inhibiting the conversion of testosterone to dihydrotestosterone

Absorption

Bioavailability: 65%

Onset: 6 months (BPH); >3 months (hair loss)

Peak plasma time: 2-6 hours

Distribution

Protein bound: 90%

Vd: 76 L

Metabolism

Hepatic CYP3A4

Metabolites: t-butyl side chain monohydroxylate, monocarboxylic acid metabolite (active)

Elimination

Half-life: 6 hours

Excretion: Feces (57%); urine (39%)