5 alpha-Reductase Inhibition in Hair Growth

Edwin S. Epstein, M.D.
Stuart Medical Group, Richmond, VA, USA.

SUMMARY of Dr. Epstein’s Abstract from his presentation at the International Society of Hair Restoration Surgery, 2005 – Sydney, Australia

Dihydrotestosterone (DHT) is known to be the more potent androgen in both Benign Prostatic Hyperplasia (BPH) and in Androgenetic Alopecia (AGA). Testosterone is converted to DHT by the enzyme 5-α reductase in several organs including the prostate, hair follicles, skin, liver and sebaceous glands. 5-α reductase exists in two isoforms: type 1 and type 2. Type 2 is the predominant enzyme in prostate and hair follicles. Finasteride, approved in 1992, inhibits the type 2 isoenzyme and is available in two doses: 1mg dose for AGA, and 5mg for BPH. Dutasteride, approved in January 2003 to treat BPH, is a dual inhibitor of both isoenzymes.

In current the study, men ages 21-45 received dutasteride (0.01mg, 0.1mg, 0.5mg, 2.5mg), finasteride 5mg, or placebo.

Results showed the following:

• Dutasteride seemed to have an earlier onset of effect than Finasteride
• Dutasteride 2.5mg appeared to be significantly more effective than Dutasteride 0.5mg.
• The effects of Dutasteride 0.5mg were comparable to Finasteride 5mg.

The side effect profile was difficult to interpret. All of the data is presented in such limited terms that make any interpretation difficult.

Dutasteride appears to work faster than finasteride in the treatment of androgenetic alopecia and clearly is more effective in lowering DHT levels. Because there is no human model for combined type I and II 5-α reductase inhibition (as there is with type II) long-term usage should be viewed cautiously.

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