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5-alpha reductase inhibitor (Type I and II) Pregnancy: Not for use in women. Absorbed through skin — pregnant women avoid handling.

Dutasteride

Brand names: Avodart, Combodart (with tamsulosin)

Adult dose

Dose: 500 micrograms once daily
Route: Oral (swallow whole — do not chew, dissolves too slowly, GI irritation from capsule contents)
Frequency: Once daily
Max: 500 micrograms/day
BPH: 500 micrograms OD. Effect seen after 3–6 months. Lowers PSA by ~50% after 6 months. Combodart (dutasteride 500 mcg + tamsulosin 400 mcg) available as combination capsule for BPH.

Paediatric dose

Route: Not applicable
Frequency: Not for children or women
Max: Not applicable
Not for use in women or children. Women of childbearing potential must not handle crushed capsules (risk of feminisation of male fetus).

Dose adjustments

Renal

No dose adjustment required.

Hepatic

Use with caution in severe hepatic impairment.

Clinical pearls

  • Inhibits both type I and II 5-alpha reductase (vs finasteride type II only) — more complete DHT suppression
  • PSA halved — same as finasteride — double measured PSA for cancer screening
  • Combination with alpha-blocker reduces BPH symptom progression better than monotherapy (CombAT trial)
  • Half-life: ~5 weeks — effects persist months after stopping
  • Blood donation contraindicated for 6 months after stopping (risk to pregnant recipient)

Contraindications

  • Women and children
  • Hypersensitivity to 5-alpha reductase inhibitors

Side effects

  • Sexual dysfunction (reduced libido, erectile dysfunction, ejaculatory disorders)
  • Gynaecomastia and breast tenderness
  • Reduced PSA (interpret cautiously for cancer screening)
  • Prostate cancer (possible increased risk of high-grade cancer — unclear)

Interactions

  • CYP3A4 inhibitors — increased dutasteride levels
  • Tamsulosin (Combodart) — additive BPH treatment (no additional interaction)

Monitoring

  • PSA (adjusted reference ranges)
  • Urinary symptoms (IPSS)
  • Sexual function

Reference: BNFc; BNF; NICE NG118; EAU BPH Guidelines; CombAT Trial. Verify against your local formulary and the latest BNF before prescribing.

Related

Curated clinical cross-links plus same-class fallbacks.

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