Q: My friend is taking Avodart, he bought it over the internet. Is it safe to take? — T.G., Denver, Colorado

A: Avodart (dutasteride 0.5mg) was approved by the FDA for the treatment of prostate enlargement in men in 2002. Avodart has not been approved for the treatment of androgenetic hair loss, although physicians can use an approved medication in ways other than for which it was specifically approved. That said, the use of dutasteride certainly requires a doctor’s supervision.

Like finasteride (the active ingredient in Proscar and Propecia), dutasteride blocks the enzyme 5-alpha reductase that converts testosterone to DHT (DHT is a key hormone that causes hair loss). However, unlike finasteride, which only inhibits the Type I form of the enzyme, dutasteride inhibits both the Type I and Type II forms. This combined effect lowers circulating DHT more with dutasteride than with finasteride, but also increases the incidence of its side effects.

The Type II form of the enzyme (blocked by finasteride) is found predominantly in the hair follicle. The Type I form of the enzyme has been found in the scalp and sebaceous glands, and many other parts of the body, but its exact role in hair growth has not been determined. It is felt that dutasteride’s ability to dramatically lower serum levels of DHT is what makes it a more potent medication in hair loss.

When considering the safety of dutasteride, one should consider the following:

• It acts on other parts of the body besides the hair follicle.
• Unlike finasteride, where families that had a deficiency of the Type II 5-alpha reductase enzyme were followed for years without any adverse effects, there is no natural biologic model to show the safety of dutasteride.
• Dutasteride has been approved for prostate enlargement in an older male population. It is not approved for hair loss and, in fact, the clinical trials for hair loss were discontinued, so there is no safety data for its use in younger patients. There is a greater incidence of sexual side effects with dutasteride compared to finasteride.
• The 1/2 life of dutasteride is 5 weeks compared to 6-8 hours for finasteride. Serum concentrations of dutasteride are detectable up to 4-6 months after discontinuation of treatment.