Dutasteride inhibits the enzyme 5-alpha reductase, which is responsible for converting testosterone into dihydrotestosterone (DHT). There are two isoforms of 5-alpha reductase: type 1 and type 2. Dutasteride is unique in that it inhibits both isoforms, making it a dual 5-alpha reductase inhibitor. The mechanism of action involves:

1. Reduction of DHT Levels:
   • By inhibiting 5-alpha reductase, dutasteride significantly reduces serum and intraprostatic DHT levels.
   • Lower DHT levels lead to shrinkage of the prostate gland, improving urinary symptoms associated with BPH.
2. Prevention of Prostate Growth:
   • Dutasteride not only alleviates symptoms but also prevents further prostate enlargement, reducing the risk of complications such as acute urinary retention and the need for surgery.
3. Hair Loss Treatment:
   • In androgenetic alopecia, dutasteride reduces scalp DHT levels, slowing hair loss and promoting hair regrowth.

Dutasteride is approved for the following conditions:

1. Benign Prostatic Hyperplasia (BPH):
   • Treatment of symptomatic BPH to improve urinary flow and reduce symptoms such as:
     • Difficulty starting urination
     • Weak urine stream
     • Frequent urination (especially at night)
     • Incomplete bladder emptying
   • Prevention of disease progression, including acute urinary retention and the need for surgical intervention.
2. Androgenetic Alopecia (Male Pattern Hair Loss):

Off-label use for the treatment of male pattern hair loss, particularly in patients who do not respond to finasteride

The dosage of dutasteride varies depending on the indication. Below are general guidelines:

1. Benign Prostatic Hyperplasia (BPH):
   • Standard Dose: 0.5 mg taken orally once daily.
   • Administration: Swallow the capsule whole; do not crush or chew.
2. Androgenetic Alopecia (Off-Label Use):
   • Standard Dose: 0.5 mg taken orally once daily.
   • Duration: Long-term use is required to maintain results.
3. Special Populations:
   • Elderly: No dose adjustment is required.
   • Renal Impairment: No dose adjustment is needed.
   • Hepatic Impairment: Use with caution in patients with severe hepatic impairment.

Dutasteride is generally well-tolerated, but some side effects may occur. These include:

1. Common Side Effects:
   • Decreased libido
   • Erectile dysfunction
   • Ejaculation disorders (e.g., reduced semen volume)
   • Gynecomastia (enlargement of breast tissue in men)
2. Less Common Side Effects:
   • Dizziness
   • Headache
   • Skin rash
3. Rare but Serious Side Effects:
   • Allergic Reactions: Rare cases of angioedema (swelling of the face, lips, or tongue).
   • Depression: Rare reports of mood changes or depression.
   • Prostate Cancer Risk: Dutasteride may affect prostate-specific antigen (PSA) levels, complicating prostate cancer screening.

1. Contraindications:
   • Hypersensitivity to dutasteride or any component of the formulation.
   • Use in women, particularly during pregnancy, due to the risk of fetal harm.
2. Warnings:
   • Pregnancy Risk: Dutasteride is teratogenic and can cause abnormalities in male fetal genitalia. Women who are pregnant or may become pregnant should not handle crushed or broken dutasteride capsules.
   • PSA Monitoring: Dutasteride reduces PSA levels by approximately 50%. Adjustments to PSA values may be necessary when monitoring for prostate cancer.
   • Blood Donation: Patients should not donate blood until at least 6 months after their last dose to prevent exposure to pregnant women.
3. Monitoring:
   • Regular monitoring of BPH symptoms and urinary flow.
   • PSA testing for prostate cancer screening, with adjustments for dutasteride’s effect on PSA levels.

Dutasteride interacts with several medications, including:

1. CYP3A4 Inhibitors (e.g., ketoconazole, ritonavir): May increase dutasteride levels, increasing the risk of side effects.
2. Alpha-Blockers (e.g., tamsulosin): Often used in combination with dutasteride for BPH, but monitor for additive hypotensive effects.
3. Other 5-Alpha Reductase Inhibitors (e.g., finasteride): Concurrent use is not recommended.

Dutasteride is available under its generic name as well as brand names. Some common formulations include:

• Generic Name: Dutasteride
• Brand Names: Avodart (commonly used in the US and UK), and others depending on the region.