A novel finasteride 0.25% topical solution for androgenetic alopecia: pharmacokinetics and effects on plasma androgen levels in healthy male volunteers

Objective: Finasteride, a selective inhibitor of type 2 5-alpha reductase isoenzyme, inhibits the conversion of testosterone to dihydrotestosterone (DHT) and is indicated in the treatment of male androgenetic alopecia. The study objective was to evaluate a newly developed finasteride 0.25% topical solution in comparison to the marketed finasteride 1 mg tablet, with respect to finasteride pharmacokinetics and suppressive effects on plasma DHT. Methods: 24 healthy men with androgenetic alopecia were randomized in a single center, open-label, parallel-group, exploratory study, and received either multiple scalp applications of the topical solution b.i.d. or oral doses of the reference tablet o.d. for 7 days. Plasma finasteride, testosterone and DHT concentrations were determined. Results: After multiple doses, mean (SD) finasteride C-max and AUC(0-t) corresponded to 0.46 +/- 0.28 ng/mL and 6.64 +/- 7.50 ng/mLxh for the topical solution and to 6.86 +/- 1.78 ng/mL and 57.93 +/- 29.38 ng/mLxh for the tablet. Plasma DHT was reduced by similar to 68 - 75% with the topical solution and by similar to 62 - 72% with the tablet. No relevant changes occurred for plasma testosterone with either treatment. No clinically significant adverse events occurred. Conclusions: A strong and similar inhibition of plasma DHT was found after 1 week of treatment with the topical and tablet finasteride formulations, albeit finasteride plasma exposure was significantly lower with the topical than with the oral product (p < 0.0001).