Finasteride specifically inhibits the type 2 isoform of 5-alpha reductase, an enzyme responsible for converting testosterone into dihydrotestosterone (DHT). The mechanism of action involves:

1. Reduction of DHT Levels:
   • By inhibiting 5-alpha reductase type 2, finasteride significantly reduces serum and intraprostatic DHT levels.
   • Lower DHT levels lead to shrinkage of the prostate gland, improving urinary symptoms associated with BPH.
2. Prevention of Prostate Growth:
   • Finasteride not only alleviates symptoms but also prevents further prostate enlargement, reducing the risk of complications such as acute urinary retention and the need for surgery.
3. Hair Loss Treatment:

In androgenetic alopecia, finasteride reduces scalp DHT levels, slowing hair loss and promoting hair regrowth

Finasteride is approved for the following conditions:

1. Benign Prostatic Hyperplasia (BPH):
   • Treatment of symptomatic BPH to improve urinary flow and reduce symptoms such as:
     • Difficulty starting urination
     • Weak urine stream
     • Frequent urination (especially at night)
     • Incomplete bladder emptying
   • Prevention of disease progression, including acute urinary retention and the need for surgical intervention.
2. Androgenetic Alopecia (Male Pattern Hair Loss):
   • Treatment of male pattern hair loss in men to slow hair loss and promote hair regrowth.

The dosage of finasteride varies depending on the indication. Below are general guidelines:

1. Benign Prostatic Hyperplasia (BPH):
   • Standard Dose: 5 mg taken orally once daily.
   • Administration: Swallow the tablet whole; do not crush or chew.
2. Androgenetic Alopecia (Male Pattern Hair Loss):
   • Standard Dose: 1 mg taken orally once daily.
   • Duration: Long-term use is required to maintain results.
3. Special Populations:
   • Elderly: No dose adjustment is required.
   • Renal Impairment: No dose adjustment is needed.
   • Hepatic Impairment: Use with caution in patients with severe hepatic impairment.

Finasteride is generally well-tolerated, but some side effects may occur. These include:

1. Common Side Effects:
   • Decreased libido
   • Erectile dysfunction
   • Ejaculation disorders (e.g., reduced semen volume)
   • Gynecomastia (enlargement of breast tissue in men)
2. Less Common Side Effects:
   • Dizziness
   • Headache
   • Skin rash
3. Rare but Serious Side Effects:
   • Allergic Reactions: Rare cases of angioedema (swelling of the face, lips, or tongue).
   • Depression: Rare reports of mood changes or depression.

Prostate Cancer Risk: Finasteride may affect prostate-specific antigen (PSA) levels, complicating prostate cancer screening

1. • Pregnancy Risk: Finasteride is teratogenic and can cause abnormalities in male fetal genitalia. Women who are pregnant or may become pregnant should not handle crushed or broken finasteride tablets.
   • PSA Monitoring: Finasteride reduces PSA levels by approximately 50%. Adjustments to PSA values may be necessary when monitoring for prostate cancer.
   • Blood Donation: Patients should not donate blood until at least 1 month after their last dose to prevent exposure to pregnant women.
2. Monitoring:
   • Regular monitoring of BPH symptoms and urinary flow.

PSA testing for prostate cancer screening, with adjustments for finasteride’s effect on PSA levels

Finasteride interacts with several medications, including:

1. CYP3A4 Inhibitors (e.g., ketoconazole, ritonavir): May increase finasteride levels, increasing the risk of side effects.
2. Alpha-Blockers (e.g., tamsulosin): Often used in combination with finasteride for BPH, but monitor for additive hypotensive effects.
3. Other 5-Alpha Reductase Inhibitors (e.g., dutasteride): Concurrent use is not recommended.

Finasteride is available under its generic name as well as brand names. Some common formulations include:

• Generic Name: Finasteride
• Brand Names: Proscar (5 mg for BPH), Propecia (1 mg for male pattern hair loss), and others depending on the region.