Finasteride
Finasteride
Generic Name
Finasteride
Mechanism
Finasteride blocks the type II and type III 5‑α‑reductase enzymes, thereby:
• Reducing conversion of testosterone to dihydrotestosterone (DHT) by ~70 % in the prostate and 90 % in scalp hair follicles.
• Decreasing intraprostatic DHT, which lowers prostate tissue volume and alleviates lower urinary tract symptoms (LUTS).
• Lowering scalp DHT, which mitigates miniaturization of hair follicles, slowing hair loss and stimulating regrowth.
The inhibition is dose‑specific: 1 mg produces ~50 % DHT reduction in the prostate, whereas 5 mg yields ~70 % reduction.
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Pharmacokinetics
| Parameter | Data (typical values) |
| Absorption | Rapid; peak plasma concentration (Cmax) 5–8 h post‑dose. |
| Bioavailability | ~60 % after oral administration (minimal first‑pass). |
| Distribution | Volume of distribution ≈55 L. Highly lipophilic; distributes to prostate and skin. |
| Metabolism | Primarily glucuronidation (UGT2B7); minimal CYP involvement. |
| Elimination | Half‑life 5–7 days (steady‑state ~18 days); 95 % eliminated unchanged in feces. |
| Protein binding | ~90 % (primarily albumin). |
| Renal/hepatic impairment | No dose adjustment needed. |
> Key PK note: Long half‑life necessitates cessation well before potential teratogenic risk in pregnancy.
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Indications
- Benign Prostatic Hyperplasia (BPH)
- 1 mg daily for ≤2 years; added to α‑blocker for refractory LUTS.
- Androgenetic Alopecia (male)
- 5 mg daily for ≥ 12 weeks; continue indefinitely for maintenance.
*Not indicated in women, children, or patients who might become pregnant.*
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Contraindications
| Contraindication | Reason |
| Pregnancy | Teratogenic; causes feminization of male fetus |
| History of severe hypersensitivity | Allergic reactions reported (urticaria, angioedema) |
| Women of childbearing potential | Must avoid; use effective contraception |
Warnings
• Teratogenicity: Must be discontinued at least 3 months before potential pregnancy; pregnancy test if conception possible.
• Sexual dysfunction: Low incidence of decreased libido, ejaculatory disorders, erectile dysfunction; monitor and discuss risks.
• Psychiatric effects: Rare reports of depression/anxiety; consider baseline mental health assessment.
• Myocardial infarction risk: Some evidence suggests reduced risk of incident MI in men taking finasteride vs. placebo.
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Dosing
- BPH
- 1 mg (1 mg film‑coated tablet) once daily, 30 min before bedtime.
- Continuation beyond 12 months should be guided by symptom improvement and PSA monitoring.
- Add-on: Combination with α‑blockers (e.g., tamsulosin) for refractory LUTS.
- Androgenetic Alopecia
- 5 mg oral tablet once daily, preferably at the same time each day.
- Minimum 3 months of therapy to evaluate efficacy; consider ongoing therapy for sustained benefit.
*Take the tablet with or without food. Swallow whole.*
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Adverse Effects
Common (≤10 %)
• Decreased libido, erectile dysfunction, reduced ejaculate volume
• Headache, dizziness
• Nasal congestion, mild urinary discomfort
Serious (≤1 %)
• Sexual dysfunction (persistent, impacting quality of life)
• Breast tenderness/swelling (rare)
• Allergic reactions (angioedema, rash)
• Depressive symptoms (rare)
• Possible increased risk of high‑grade prostate cancer (controversial)
> Note: The incidence of severe DHT inhibition‑related effects is low but should be addressed during first visits.
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Monitoring
- PSA in BPH patients: Evaluate every 6–12 months; adjust for the ~50 % suppression effect.
- Symptom scoring (IPSS) at 3, 6, and 12 months to assess LUTS improvement.
- Urine flow (Qmax) if clinically indicated.
- Baseline and periodic sexual health assessment for counseling.
- Pregnancy status: Verify with women of childbearing potential prior to initiation and during therapy.
- Eosinophil count if dermatologic reactions suspected.
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Clinical Pearls
1. PSA Adjustment – Finasteride halves PSA values; divide PSA by 0.5 when interpreting for prostate cancer risk.
2. Hair Regrowth Timeline – Maximal response observed after 4–6 months; continuous use maintains benefits—discontinuation results in loss of effect within 3–6 months.
3. Combination Therapy in BPH – Adding finasteride to an α‑blocker yields synergistic improvement in bladder outlet obstruction versus monotherapy.
4. Teratogenic Window – The drug’s long half‑life requires discontinuation ≥3 months before pregnancy; use reliable contraception throughout treatment.
5. Patient Education – Screen for baseline sexual function; discuss potential side‑effects proactively to improve adherence.
6. Monitoring for High‑Grade Prostate Cancer – Although overall prostate cancer risk is reduced, some data suggest a possible rise in high‑grade lesions; discuss implications if PSA returns rise unprotected by finasteride therapy.
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• *For detailed prescribing information, refer to the FDA product label and peer‑reviewed literature such as the Prostate Cancer Prevention Trial (PCPT) and the Male Pattern Hair Loss Studies.*