Finasteride is a synthetic 4-azasteroid compound that functions as a specific inhibitor of type II 5α-reductase, the enzyme responsible for converting testosterone to dihydrotestosterone (DHT). DHT plays a central role in the pathophysiology of benign prostatic hyperplasia (BPH) and androgenetic alopecia (male pattern hair loss). Finasteride is approved for the treatment of BPH under the brand name Proscar (5 mg), and for male pattern hair loss under the brand name Propecia (1 mg).
Pharmacological Classification
-
Therapeutic class: 5α-reductase inhibitor
-
Pharmacologic class: Antiandrogen
-
ATC code:
-
G04CB01 (for BPH)
-
D11AX10 (for alopecia)
-
Mechanism of Action
Finasteride competitively and selectively inhibits type II 5α-reductase, the enzyme that converts testosterone to dihydrotestosterone (DHT) in the prostate, scalp, and other androgen-sensitive tissues. By lowering DHT levels:
-
In the prostate, it reduces prostatic volume, relieves urinary obstruction, and improves urine flow in BPH.
-
In the scalp, it reduces miniaturization of hair follicles, slows hair loss progression, and may promote regrowth in androgenetic alopecia.
Finasteride does not inhibit type I 5α-reductase, which is expressed in the liver and skin, unlike dutasteride (which inhibits both).
Indications
Benign Prostatic Hyperplasia (BPH)
-
Reduces prostate volume (~20–30% after 6–12 months)
-
Improves urinary flow
-
Reduces risk of acute urinary retention (AUR)
-
Decreases need for prostate surgery
-
Often combined with alpha-blockers (e.g., tamsulosin) in moderate to severe BPH
Androgenetic Alopecia
-
Male pattern baldness in men aged 18–41 years with mild to moderate hair loss at the vertex and anterior mid-scalp
-
Increases hair count and slows progression of baldness
-
Effects become noticeable after 3–6 months of daily use
Dosage and Administration
Benign Prostatic Hyperplasia (BPH)
-
5 mg once daily, with or without food
-
Symptomatic improvement may take 6 months or longer
-
Can be used as monotherapy or with an alpha-blocker
Male Pattern Hair Loss
-
1 mg once daily, with or without food
-
Continued treatment required to maintain benefit
-
Discontinuation reverses effects within 12 months
Missed dose
-
Take as soon as remembered, but do not double the dose
-
Daily consistency is key for efficacy
Pharmacokinetics
-
Absorption: ~80% orally bioavailable
-
Peak plasma levels: 1–2 hours post-dose
-
Half-life: ~5–6 hours (younger men); up to 8 hours in elderly
-
Protein binding: ~93%
-
Metabolism: Hepatic (CYP3A4 pathway)
-
Excretion: 39% urine (metabolites), 57% feces
Contraindications
-
Women: Particularly during pregnancy or those who may become pregnant – risk of fetal genital abnormalities in male fetus
-
Children and adolescents: Not indicated
-
Hypersensitivity to finasteride or any of its components
Warnings and Precautions
-
Pregnant women should not handle crushed or broken tablets due to transdermal absorption risk
-
May mask PSA levels: Finasteride lowers serum PSA by ~50%, potentially masking early detection of prostate cancer; adjusted PSA interpretation is necessary
-
Risk of high-grade prostate cancer: Some data (e.g., PCPT trial) suggested a small increased risk of aggressive prostate cancer
-
Depression and suicidal ideation: Post-marketing reports have linked finasteride to depressive symptoms
-
Reduced fertility: Rare cases of decreased sperm count and quality reported
Adverse Effects
BPH (5 mg dose)
-
Decreased libido (1.8–6%)
-
Erectile dysfunction (3–6%)
-
Ejaculation disorders (e.g., decreased volume, 0.8–2%)
-
Breast tenderness or enlargement (gynecomastia)
-
Rash, dizziness, weakness (less common)
Hair Loss (1 mg dose)
-
Sexual dysfunction (1–2%)
-
Depression (rare but serious concern)
-
Anxiety, fatigue (anecdotally reported)
-
Post-finasteride syndrome (PFS): Persistent sexual, neurological, or cognitive side effects after discontinuation (not formally recognized as a syndrome by all regulatory bodies)
Drug Interactions
Finasteride has low potential for drug interactions, but caution is advised with:
-
CYP3A4 inducers (e.g., carbamazepine, rifampicin): May decrease plasma concentration (no dose adjustment usually needed)
-
CYP3A4 inhibitors (e.g., ketoconazole): May increase finasteride levels slightly
-
No significant interaction with digoxin, propranolol, theophylline, warfarin
Monitoring Parameters
-
PSA levels: Baseline and during therapy
-
Urinary symptoms: In BPH, assess IPSS (International Prostate Symptom Score)
-
Prostate size (ultrasound or DRE)
-
Mood changes: Evaluate for depression or suicidal thoughts
-
Sexual function: Discuss and assess changes if relevant
Use in Special Populations
Pregnancy
-
Category X: Absolutely contraindicated
-
Can cause feminization of male fetus genitalia (hypospadias, ambiguous genitalia)
-
Women of childbearing age should not handle broken tablets
Lactation
-
Not indicated in women
Elderly
-
No dose adjustment needed
-
Half-life may be slightly prolonged
Renal Impairment
-
No dose adjustment required
Hepatic Impairment
-
Use with caution (metabolized in liver), but no specific adjustment guidelines available
Patient Counseling Points
-
Take at the same time each day
-
Sexual side effects may occur and could persist after stopping
-
Full effects may take 3 to 6 months to appear
-
Tablets must be swallowed whole
-
Women who are pregnant should not touch broken tablets
-
Report any symptoms of breast changes, depression, or ejaculatory disorders
Special Considerations
-
Combining with minoxidil: For hair loss, combination with topical minoxidil may have additive effects
-
Discontinuation: Results in reversal of benefits within 6–12 months
-
Prostate cancer screening: PSA levels are halved, so values must be doubled to interpret correctly
-
Post-Finasteride Syndrome: Though not universally accepted, some patients report persistent issues even after stopping the drug. Research is ongoing
Brand Names
-
Propecia (1 mg tablets – hair loss)
-
Proscar (5 mg tablets – BPH)
-
Generic formulations widely available
No comments:
Post a Comment