Finasteride

• Benign Prostatic Hyperplasia (BPH)
• Male Pattern Hair Loss
• Prostate Enlargement
• Androgenetic Alopecia

Finasteride is a 5-alpha reductase inhibitor used for the treatment of benign prostatic hyperplasia (BPH) and male pattern hair loss (androgenetic alopecia). This medication works by blocking the conversion of testosterone to dihydrotestosterone (DHT), a hormone responsible for prostate growth and hair follicle miniaturization.

Mechanism of Action

Finasteride selectively inhibits the type II 5-alpha reductase enzyme, which is responsible for converting testosterone to dihydrotestosterone (DHT) in the prostate gland, hair follicles, and skin. DHT is a more potent androgen than testosterone and is the primary androgen responsible for prostate growth and for the progressive miniaturization of hair follicles in androgenetic alopecia. By inhibiting type II 5-alpha reductase, finasteride reduces serum and tissue DHT levels by approximately 70%, leading to prostate volume reduction (about 20% over 6-12 months) and reversal or prevention of hair follicle miniaturization. Unlike dutasteride, finasteride does not significantly inhibit type I 5-alpha reductase.

Available Formulations

Finasteride is available as oral tablets in two strengths: 1 mg (for hair loss) and 5 mg (for BPH). The different doses reflect the different approved indications and should not be used interchangeably. Generic formulations are available for both strengths. The tablets can be taken with or without food.

Medical Uses

Finasteride 5 mg is FDA-approved for the treatment of symptomatic benign prostatic hyperplasia to improve symptoms, reduce the risk of acute urinary retention, and reduce the need for surgery. Finasteride 1 mg is approved for the treatment of male pattern hair loss (androgenetic alopecia) at the vertex and anterior mid-scalp area. Clinical trials have demonstrated sustained improvement in urinary symptoms, prostate volume reduction, and hair regrowth or prevention of further hair loss.

Dosing Guidelines

For BPH, the dose is 5 mg once daily, which can be taken with or without food. Treatment should continue for at least 6-12 months to assess therapeutic response. For male pattern hair loss, the dose is 1 mg once daily. Three months or more of daily use may be required before benefit is observed. Continued use is necessary to sustain benefit; stopping the medication results in reversal of effects over 12 months.

Important Safety Information

Finasteride carries a warning for increased risk of high-grade prostate cancer (Gleason score 8-10) based on PCPT trial data. PSA levels decrease by approximately 50% during treatment; measured PSA values should be doubled for comparison to normal ranges or previous values. Pregnant women should not handle crushed or broken tablets due to risk of hypospadias in male fetuses. Reports of persistent sexual side effects (decreased libido, erectile dysfunction, decreased ejaculate volume) continuing after discontinuation have been received.

Drug Interactions

Finasteride is metabolized by CYP3A4, but no clinically significant drug interactions have been identified with commonly used medications. No dose adjustment is needed when used with other commonly prescribed medications. Finasteride does not affect the pharmacokinetics of drugs metabolized by CYP enzymes.

Special Populations

Finasteride is contraindicated in women who are or may become pregnant due to risk of hypospadias in male fetuses. It is not indicated for use in women or children. Men taking finasteride should not donate blood until at least 1 month after the last dose to prevent exposure of pregnant transfusion recipients. Elderly patients do not require dose adjustment. No dose adjustment is needed for renal impairment. Use with caution in hepatic impairment; decreased drug clearance may occur.