If a patient complains of gynecomastia on Proscar (finasteride), can we prescribe dutasteride instead?

Switching from Finasteride to Dutasteride for Gynecomastia

Switching from finasteride to dutasteride is not recommended for patients experiencing gynecomastia, as both medications carry similar risks of gynecomastia. 1

Gynecomastia Risk with 5α-Reductase Inhibitors

Both finasteride (Proscar) and dutasteride are 5α-reductase inhibitors (5-ARIs) that can cause gynecomastia:

• Gynecomastia occurs in approximately 2.3% of patients taking 5-ARIs compared to 0.74% on placebo, with a relative risk of 2.13 1
• Long-term treatment with 5-ARIs shows gynecomastia rates of 4.5% versus 2.8% for placebo 1
• The FDA drug label for dutasteride specifically lists breast disorders (including gynecomastia) as a common adverse effect 2

Comparison of Finasteride vs. Dutasteride Side Effects

Both medications work through similar mechanisms but with key differences:

• Finasteride selectively inhibits the 5-AR type II isoenzyme
• Dutasteride inhibits both types I and II isoenzymes 1
• This difference results in dutasteride reducing serum DHT by approximately 95% compared to 70% with finasteride 1

Despite these pharmacological differences, clinical evidence shows:

• Both medications have similar adverse effect profiles regarding sexual dysfunction and gynecomastia 1, 3
• Dutasteride may actually have a higher risk of gynecomastia than finasteride according to some studies 4

Management Recommendations for Gynecomastia

For patients experiencing gynecomastia on finasteride:

1. Discontinue the 5-ARI therapy - This is the first-line approach as continued exposure may lead to persistent gynecomastia 3, 5

2. Consider alternative BPH treatments if appropriate:

   • Alpha-blockers (tamsulosin, alfuzosin, etc.) which do not have significant gynecomastia risk 1
   • Surgical options for BPH if medical therapy is inadequate

3. For persistent gynecomastia:

   • Consider selective estrogen receptor modulators like tamoxifen for symptomatic relief 6
   • Surgical correction (mammoplasty) may be necessary for established fibrotic gynecomastia 5

Important Considerations and Monitoring

• Gynecomastia may persist even after discontinuation of 5-ARIs 7, 5
• Early intervention when gynecomastia first develops may prevent irreversible fibrotic changes 5
• Regular assessment of breast tissue during treatment with any 5-ARI is recommended 3

Pitfalls to Avoid

• Do not switch between 5-ARIs for gynecomastia - Both medications carry similar risks of this side effect
• Do not ignore patient complaints - Gynecomastia can significantly impact quality of life and may become irreversible if not addressed promptly
• Do not continue 5-ARI therapy without discussing alternatives - There are other effective options for BPH management without this side effect
• Do not assume gynecomastia will resolve spontaneously - Some cases may persist despite medication discontinuation 5

In conclusion, patients experiencing gynecomastia on finasteride should not be switched to dutasteride, as both medications share this adverse effect profile. Instead, discontinuation of 5-ARI therapy and consideration of alternative treatments for BPH is recommended.