In this phase II, dose-ranging study, 2.5-mg dutasteride was superior to 5-mg finasteride in improving scalp hair growth in men between ages 21 and 45 years with MPHL as judged by target area hair counts, expert panel assessment, and investigator assessment at 12 and 24 weeks.
In a test area at 24 weeks, results showed:
Placebo −32.3 hairs
Finasteride 5mg 75.6 hairs
Dutasteride 0.1 mg 78.5 hairs
Dutasteride 0.5 mg 94.6 hairs
Dutasteride 2.5 mg 109.6 hairs
Dutasteride 2.5mg vs. 0.5mg
The 2.5-mg dutasteride dose was consistently superior to 0.5-mg dutasteride in promoting scalp hair growth. The 2.5-mg dose was also better than the 0.5-mg dose at suppressing scalp DHT (79% vs. 51%), whereas it was only marginally better at suppressing serum DHT (96% vs. 92%). This difference in the dose-response of serum and scalp DHT to inhibition with dutasteride is likely to be due to the greater contribution of type 1 5α-reductase to scalp DHT concentrations.
Finasteride 5mg vs. Dutasteride 0.1mg
5 mg finasteride suppressed scalp DHT to a similar degree as 0.1 mg dutasteride group (41% and 32%, respectively). Many of the clinical effects (hair count changes, global panel assessment, and investigator assessment) were also similar in these two groups, supporting the similarity in scalp suppression between 5-mg finasteride and 0.1-mg dutasteride.
Both dutasteride and finasteride were well tolerated in this phase II study, and no new safety concerns have arisen in any of the phase II and phase III studies of dutasteride given at doses up to 5 mg daily (the 5-mg dose was used in a phase II study for BPH).
There were no significant differences in side effects, serious adverse events, or withdrawals due to adverse events among any of the treatment groups, including placebo. In total, 11 subjects withdrew because of adverse events: 3 were in the placebo group (irritable bowel syndrome and impotency), 7 in the dutasteride 0.1 mg group (decreased libido, malaise and fatigue, mood disorders, skin disorders, injuries caused by trauma, and gastrointestinal- and neurology-related complaints) and 1 in the dutasteride 0.5 mg group (gastrointestinal discomfort and pain).
Decreased libido was noted in:
2 subjects in the placebo group
2 subjects in each of the 0.05-mg and 0.1-mg dutasteride groups
1 subject in the 0.5-mg dutasteride group
9 subjects in the 2.5 mg dutasteride group
3 subjects in the finasteride group
Of the 9 subjects with decreased libido in the 2.5-mg dutasteride group:
4 resolved while receiving therapy
1 resolved within 3 weeks
1 resolved within 8 weeks of stopping drug therapy
1 subject, decreased libido continued after therapy had been stopped and was presumed by the subject to be unrelated to the trial or drug therapy
Concerning possible sexual adverse events, there was no evidence in the present study that either dutasteride or finasteride was associated with impotence. However, 9 men in the 2.5-mg dutasteride group complained of decreased libido, compared with 1 man in the 0.5-mg dutasteride group and 3 men in the finasteride group. As with previous studies with finasteride, this adverse event was characterized as either mild or moderate in severity and often resolved with continuation of the medication. In the 4-year follow-up of the phase III trials in BPH, dutasteride (0.5 mg) was well tolerated and the incidence of the most common sexual adverse events was low and tended to decrease over time.
The only subject to develop gynecomastia was in the placebo group.
Duration of Effects
The serum half-life of finasteride is 6 to 8 hours. Dutasteride has a serum half-life of approximately 4 weeks, and this long half-life was evident in the persistent suppression of DHT with the 0.5-mg and 2.5-mg doses after dutasteride treatment was stopped. Because of this long half-life, men being treated with dutasteride should not donate blood until at least 6 months past their last dose to prevent administration to a pregnant female transfusion recipient.