Dutasteride and Finasteride Should Not Be Used Together
Dutasteride (Avodart) and finasteride (Proscar) should not be used concurrently as they have the same mechanism of action and combining them provides no additional clinical benefit while potentially increasing the risk of adverse effects. 1
Mechanism of Action and Overlap
- Both medications are 5-alpha-reductase inhibitors (5-ARIs) that block the conversion of testosterone to dihydrotestosterone (DHT) 1, 2
- Finasteride selectively inhibits the Type 2 isoenzyme of 5-alpha-reductase, while dutasteride inhibits both Type 1 and Type 2 isoenzymes 3
- Since dutasteride already inhibits both isoenzymes, adding finasteride provides no additional therapeutic benefit 2, 3
Clinical Evidence
- Clinical guidelines recommend using either dutasteride or finasteride as monotherapy or in combination with an alpha-blocker (like tamsulosin) for BPH treatment, but never recommend using both 5-ARIs together 1
- The CombAT trial demonstrated the efficacy of dutasteride plus tamsulosin for BPH, but there are no clinical trials supporting the combination of two different 5-ARIs 4
- Both medications have similar efficacy profiles in BPH management with comparable prostate volume reduction, symptom improvement, and reduction in risk of acute urinary retention 3
Potential Risks of Combination
- Using both medications could potentially increase the risk of common side effects associated with 5-ARIs, including 5:
- Sexual dysfunction (erectile dysfunction, decreased libido)
- Ejaculatory disorders
- Gynecomastia
- Depression
- Both medications affect PSA levels in a similar way, reducing values by approximately 50% after 6-12 months of therapy 6
Appropriate Treatment Approaches for BPH
- For patients with moderate-to-severe lower urinary tract symptoms (LUTS) and enlarged prostate (>30cc), the recommended approach is 1:
- Monotherapy with a 5-ARI (either dutasteride or finasteride, not both)
- Combination therapy with a 5-ARI plus an alpha-blocker (e.g., dutasteride plus tamsulosin)
- Alpha blockers provide rapid symptom relief while 5-ARIs work more slowly to reduce prostate size and provide long-term benefits in reducing disease progression 1
Monitoring Considerations
- When using either dutasteride or finasteride, PSA levels should be doubled after 6-12 months of therapy to accurately assess for prostate cancer risk 6
- Both medications are contraindicated in pregnancy due to risk of birth defects in male fetuses 5
In conclusion, there is no clinical rationale for combining dutasteride and finasteride, as they work through the same mechanism and dutasteride already provides complete inhibition of both 5-alpha-reductase isoenzymes. The appropriate approach is to use either medication alone or in combination with an alpha-blocker.