Basic Science
Dutasteride (Avodart) is a potent inhibitor of both Type I and Type II isoenzymes of 5 alpha-reductase. Dutasteride was approved for the treatment of benign prostatic hyperplasia in 2002 by the FDA but does not have an indication for hair loss. At a 0.5 mg daily dosage, dutasteride reduces dihydrotestosterone (DHT) levels by over 90% as compared with finasteride, which reduces DHT by 70% at a 1 mg daily dose. As Type I 5 alpha-reductase accounts for approximately 30% of circulating DHT, dutasteride blocks the Type I isoenzyme by 60% better than finasteride.
Type I isoenzymes are found in the brain of children and adults in both sexes and may play a role in non-sex related steroid functions. Researchers have found that Type 1 5 alpha-reductase levels can help protect against breast cancer.
Dutasteride half life is 240 hours compared with 6 to 8 hours for finasteride.
CLINICAL TRIALS
Phase II clinical drug trials evaluating dutasteride in treating male pattern baldness have been completed, but Phase III trials have yet to be conducted. Some Phase II data show that at 6 months there was an increase of 96 hairs in a 1-inch circle compared with 72 hairs in the 5 mg finasteride dosage, possibly with a 33% greater efficacy. However, Phase II studies do not adhere to the same prospective, placebo controlled, double blinded standards of a Phase III trial. Also, differences that were shown at 6 months may not be maintainted thereafter.
SIDE EFFECTS
Side effects reported were impotence (5%), decreased libido (3%), ejaculation disorders (2%), and gynecomastia (1%). No integrated analysis of side effects have been undertaken. In contrast, finasteride showed most commonly decreased libido with an incidence of 1.8% with overall adverse events of 3.8%.
POSITION STATEMENT OF THE LAM INSTITUTE FOR HAIR RESTORATION ON DUTASTERIDE
Long-term safety with dutasteride has not been clarified. Treatment with dutasteride for male patterned baldness is off-label. Given the limited data on the effects of dutasteride, Dr. Lam only prescribes finasteride for his male patients. He has in the past in select cases with proper consultation prescribed dutasteride. However, in general, his current position on dutasteride is not to prescribe this medication to any new patients until further clinical trials can substantiate both efficacy and safety.
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