Dutasteride

• Benign Prostatic Hyperplasia (BPH)
• Prostate Enlargement
• Lower Urinary Tract Symptoms
• Male Pattern Hair Loss (off-label)

Dutasteride is a dual 5-alpha reductase inhibitor used for the treatment of benign prostatic hyperplasia (BPH). This medication provides more complete inhibition of dihydrotestosterone (DHT) production compared to single-type inhibitors, offering effective symptom relief and reduced risk of BPH-related complications.

Mechanism of Action

Dutasteride inhibits both type 1 and type 2 5-alpha reductase isoenzymes, which convert testosterone to dihydrotestosterone (DHT). Type 2 5-alpha reductase is predominantly expressed in the prostate and is responsible for most prostatic DHT production, while type 1 is expressed in skin and liver. By inhibiting both isoenzymes, dutasteride reduces serum DHT levels by approximately 90%, compared to 70% reduction with finasteride (which inhibits only type 2). The resulting decrease in prostatic DHT leads to prostate volume reduction (about 25% over 2 years), improved urinary symptoms, and decreased risk of acute urinary retention and need for surgery.

Available Formulations

Dutasteride is available as soft gelatin capsules containing 0.5 mg. The capsules should be swallowed whole and not chewed or opened, as contact with the capsule contents may cause oropharyngeal irritation. The medication is also available in combination with tamsulosin (Jalyn) for enhanced BPH symptom relief. The capsules should be stored at room temperature.

Medical Uses

Dutasteride is FDA-approved for the treatment of symptomatic benign prostatic hyperplasia in men with an enlarged prostate. It can be used as monotherapy or in combination with an alpha-blocker (tamsulosin) for enhanced efficacy. The CombAT trial demonstrated that combination therapy with dutasteride and tamsulosin was superior to either agent alone for symptom improvement and reduction in clinical progression. Off-label uses include androgenetic alopecia (male pattern baldness).

Dosing Guidelines

The recommended dose is 0.5 mg taken orally once daily. The medication can be taken with or without food. Improvement in BPH symptoms may be seen within 3-6 months, but maximum benefit typically requires 6-12 months of therapy. Treatment should be continued long-term; discontinuation may result in symptom return within about 6 months. The capsules should not be handled by pregnant women due to teratogenic risk.

Important Safety Information

Dutasteride carries a boxed warning about increased risk of high-grade prostate cancer, based on findings from the REDUCE trial showing higher rates of Gleason score 8-10 prostate cancers in the dutasteride group. PSA levels should be evaluated before starting therapy; dutasteride reduces PSA by approximately 50%, so values must be doubled for comparison to normal ranges. Pregnant women should not handle dutasteride capsules due to potential risk of hypospadias in male fetuses. Blood donation should be avoided for 6 months after the last dose.

Drug Interactions

CYP3A4 inhibitors (ritonavir, ketoconazole, verapamil, diltiazem) may increase dutasteride blood levels, though dose adjustment is not typically required. Dutasteride is highly protein-bound; displacement by other highly bound drugs is possible but clinical significance is unknown. No significant interactions with digoxin, warfarin, or common medications have been observed.

Special Populations

Dutasteride is contraindicated in pregnancy and in women who may become pregnant; it can cause abnormalities of external male genitalia in male fetuses. The medication is not indicated for use in women or children. Men taking dutasteride should not donate blood until 6 months after the last dose to prevent exposure of pregnant women receiving transfusions. Elderly patients do not require dose adjustment. No dose adjustment is needed for renal impairment. Use with caution in hepatic impairment; the medication is extensively metabolized in the liver.