Eun Dutasteride for AGA Results in Detail: Numbers, Subgroups, and Time Course

What the Eun trial actually tested

Dutasteride inhibits both type 1 and type 2 5-alpha reductase, the enzymes that convert testosterone to dihydrotestosterone; finasteride inhibits mainly type 2 [2].

The Eun trial randomized 153 men aged 18 to 49 with male pattern hair loss to dutasteride 0.5 mg daily or placebo for 6 months. Efficacy was judged by change in hair counts, the men's own assessment, and photographic assessment by investigators and by a panel [1].

The hair count result

Mean hair count increased by 12.2 per cm2 in the dutasteride group and 4.7 per cm2 in the placebo group from baseline to 6 months (P=.0319) [1].

Dutasteride also scored better than placebo on the men's self-assessment and on both investigator and panel photographic assessment [1].

Time course

The trial assessed results at 6 months [1].

Drug-level data come from the prostate program. On 0.5 mg daily, median serum DHT fell 85% after 1 week and 90% after 2 weeks, and 94% at 1 year [2]. The terminal half-life is about 5 weeks at steady state, with about 65% of steady state reached after 1 month and about 90% after 3 months; serum levels stay above 0.1 ng/mL for up to 4 to 6 months after the last dose [2].

Where the dutasteride versus finasteride numbers come from

A 2014 head-to-head trial randomized 917 men aged 20 to 50 to dutasteride, finasteride, or placebo for 24 weeks [3]. Hair count and width rose with dutasteride dose. Dutasteride 0.5 mg increased hair count and width in a 2.54-cm diameter area and improved frontal photographic assessment at week 24 compared with finasteride (P=.003, P=.004 and P=.002 respectively) and with placebo (all P<.001) [3]. The number and severity of adverse events were similar across groups, and the study was limited to 24 weeks [3].

An earlier trial randomized 416 men aged 21 to 45 to dutasteride 0.05, 0.1, 0.5 or 2.5 mg, finasteride 5 mg, or placebo for 24 weeks. Target area hair count rose with dutasteride dose versus placebo, and the 2.5 mg dose was superior to finasteride at 12 and 24 weeks [4]. That comparison used finasteride 5 mg, the prostate dose, not the 1 mg dose tested against dutasteride 0.5 mg in the 917-man trial [3][4].

Safety in the hair loss trials

In the Eun trial there was no major difference in adverse events between dutasteride and placebo over 6 months [1]. In the 917-man trial, adverse events were similar in number and severity across all treatment groups [3].

A meta-analysis of 15 randomized placebo-controlled trials in male androgenetic alopecia (4,495 men) found a 1.57-fold relative risk of sexual dysfunction with 5-alpha reductase inhibitors overall (95% CI 1.19 to 2.08). For finasteride 1 mg the relative risk was 1.66 (95% CI 1.20 to 2.30); for dutasteride 0.5 mg it was 1.37 (95% CI 0.81 to 2.32), which was not statistically significant, and few dutasteride trials were available [5].

The Avodart label gives rates from 2-year placebo-controlled trials in men with BPH (mean age 66), months 0 to 6: impotence 4.7% versus 1.7% on placebo, decreased libido 3.0% versus 1.4%, ejaculation disorders 1.4% versus 0.5%, and breast disorders 0.5% versus 0.2%. Rates fell after the first 6 months except breast disorders, and the label notes that sexual adverse reactions may persist after discontinuation, with the role of dutasteride in that persistence unknown [2].

The same label reports that in healthy men treated for 52 weeks, dutasteride reduced total sperm count by 23%, semen volume by 26% and sperm motility by 18% compared with placebo, while sperm concentration and morphology were unaffected and mean values stayed within the normal range. After 24 weeks off drug, total sperm count remained 23% below baseline. The clinical significance for an individual man's fertility is not known [2].

What these numbers mean for someone considering it

The Eun trial's contribution is narrow and clear: dutasteride 0.5 mg beat placebo on hair count at 6 months in 153 men, with similar short-term tolerability [1]. The head-to-head evidence against finasteride is also short, at 24 weeks, and comes from the 917-man trial at the 1 mg finasteride dose and from the 416-man trial at the 5 mg finasteride dose [3][4].

The Avodart label says men being treated with it should not donate blood until at least 6 months have passed since their last dose, to prevent giving dutasteride to a pregnant transfusion recipient [2].