Both topical and oral finasteride seem to drop the DHT levels. At the 0.25% topical dose, the drop in DHT was less than the oral; nevertheless, reports from some doctors in the field suggest that the sexual side effects still appear with the topical dose

Int J Clin Pharmacol Ther. 2016 Jan;54(1):19-27. doi: 10.5414/CP202467.

Effects of a novel finasteride 0.25% topical solution on scalp and serum dihydrotestosterone in healthy men with androgenetic alopecia.

Caserini M, Radicioni M, Leuratti C, Terragni E, Iorizzo M, Palmieri R.

Abstract

OBJECTIVE:

The effects on scalp and serum dihydrotestosterone (DHT) of different doses of a novel topical solution of 0.25% finasteride (P-3074), a type 2 5?-reductase, were investigated in men with androgenetic alopecia.

METHODS:

Two randomized, parallel-group studies were conducted. Study I: 18 men received 1 mL (2.275 mg) P-3074, applied to the scalp once a day (o.d.) or twice a day (b.i.d), or 1 mg oral tablet o.d. for 1 week. Study II: 32 men received P-3074 at the dose of 100 (0.2275 mg), 200 (0.455 mg), 300 (0.6285 mg), or 400 (0.91 mg) ?L or the vehicle o.d. for 1 week. Scalp and serum DHT and serum testosterone were evaluated at baseline and treatment end.

RESULTS:

Change from baseline in scalp DHT was -70% for P-3074 o.d. and approx. -50% for P-3074 b.i.d. and the tablet. Serum DHT decreased by 60 – 70%. The doses of 100 and 200 ?L P-3074 resulted in a -47/-52% scalp DHT reduction, similar to the 300 and 400 ?L doses (i.e., -37/-54%). A -5.6% inhibition was observed for the vehicle. Serum DHT was reduced by only -24/-26% with 100 and 200 ?L P-3074 and by -44/-48% with 300 and 400 ?L P-3074. No relevant changes occurred for serum testosterone.

CONCLUSIONS:

The novel finasteride 0.25% solution applied o.d. at the doses of 100 and 200 ?L results in an appropriate inhibition of scalp DHT potentially minimizing the untoward sexual side-effects linked to a systemic DHT reduction.