Generic Name

Dutasteride

Mechanism

Dutasteride is a potent, irreversible 5‑alpha‑reductase inhibitor that blocks both type I and type II isoenzymes responsible for converting testosterone into the more potent androgen dihydrotestosterone (DHT).
• ↓ DHT levels in peripheral tissues (prostate, scalp, hair follicles).
• ↓ stimulation of prostatic stromal/epithelial growth and androgen‑mediated hair follicle miniaturization.
• Slower reversal of effects compared with selective type II inhibitors (e.g., finasteride) due to dual‑enzyme blockade.

Pharmacokinetics

• Absorption: Oral bioavailability ~35%; peak plasma concentration 1–3 h post‑dose.
• Distribution: Highly lipophilic; extensive tissue uptake with a large volume of distribution (>700 L).
• Metabolism: Primarily hepatic via CYP3A4; metabolites are inactive.
• Elimination: Biliary excretion; terminal half‑life ≈ 4–5 days, allowing once‑daily dosing.
• Drug Interactions: CYP3A4 inhibitors (e.g., ketoconazole) may modestly raise plasma levels; no clinically significant impact on co‑administered drugs.

Indications

• Benign Prostatic Hyperplasia (BPH): Adjunct or monotherapy to relieve lower urinary tract symptoms.
• Male Pattern Baldness (androgenic alopecia): Slow‑release hair‑growth benefits in men ≥18 y.
• Transitional care for men with high DHT‑mediated disorders such as acne (off‑label, limited evidence).

Contraindications

• Contraindicated:
• Pregnancy (category X) – potential teratogenicity.
• Known hypersensitivity to dutasteride or excipients.
• Warnings:
• Teratogenic risk: female partners of men taking the drug may be exposed via bodily fluids.
• Possible suppression of prostate‑specific antigen (PSA) leading to delayed cancer detection.
• Psychosexual side‑effects: reduced libido, erectile dysfunction, ejaculatory disorders.
• Rare risk of breast tenderness/papillomatosis in men and gynecomastia.

Dosing

• Primary dosing (BPH): 0.5 mg PO once daily (no loading dose).
• Hair loss: 0.5 mg PO once daily; therapy may take 3–6 months for visible improvement.
• Administration tips: Take with or without food; consistent daily intake optimal.
• Special populations: No dose adjustment required for renal/hepatic impairment; caution in severe hepatic disease.

Adverse Effects

Common (≥5 % incidence):
• Sexual dysfunction (decreased libido, erectile dysfunction, ejaculatory distress).
• Breast tenderness/papular rash.
• Headache, dizziness, nasopharyngitis.

Serious (≤1 % incidence):
• Severe allergic reactions (angioedema).
• Secondary breast cancer (rare).
• Elevated liver enzymes; monitor baseline and periodically.
• Potential for post‑treatment flare of BPH symptoms if abruptly discontinued.

Monitoring

• PSA: Obtain baseline; repeat every 6 months to monitor prostate cancer screening.
• Serum testosterone/DHT: Optional if evaluating sexual side‑effects.
• Liver function tests (AST, ALT, bilirubin): Baseline, 3–6 months, then annually.
• Urinary flow metrics (Qmax/IPSS): Baseline and 6–12 months to gauge BPH response.
• Patient symptom diary: Sexual function, breast changes, hair growth.

Clinical Pearls

• Dual‑enzyme blockade explains why dutasteride achieves ~70–80 % more DHT suppression than finasteride, translating into better BPH symptom relief and a higher success rate in hair repigmentation.
• Pregnancy vigilance: Even a single sexual encounter can transmit teratogenic compounds; a 6‑month washout period is recommended before trying to conceive.
• PSA suppression may mask prostate cancer progression; consider imaging or prostate biopsy if PSA rises >0.2 ng/mL per month on therapy.
• Sexual side‑effects often improve after 12–18 months; discuss expectation management with patients.
• Hair loss benefits are cumulative: early discontinuation may reverse gains; steady therapy >6 months yields maximal follicular anabolic effect.
• Drug–drug interaction profile is favorable; however, avoid overlapping with other CYP3A4 inhibitor regimens to preclude systemic accumulation.

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• *All information should be verified against latest FDA prescribing data and institutional guidelines.*