Local Pharmacokinetics and Tolerability of Topically-Applied Bimatoprost to the Scalp of Male Patients With Androgenetic Alopecia.

Androgenetic alopecia (AGA) is one of the most common causes of hair loss in the male population, characterized by progressive baldness. This study was designed to evaluate the tolerability and local skin pharmacokinetics of bimatoprost in two different formulations in male subjects with AGA. Bimatoprost 1% Formulations A and B were applied topically once daily to the scalp and lateral trunk in the same subjects for 14 days. One skin biopsy from each application site was obtained on Day 14 after the final drug application. Eleven participants were dosed in this study, and their skin samples were analyzed for bimatoprost and its acid metabolite. Both formulations achieved at least a 10-fold higher bimatoprost concentration in subcutaneous fat, where the hair papilla is typically situated, than the in vitro concentration needed for maximal increased hair growth (42 ng/g) in isolated hair follicles. Both formulations showed a significant decrease in bimatoprost concentration with increasing distance from the skin surface as expected for a topically applied formulation with no significant differences between Formulations A and B. Bimatoprost acid concentrations in most samples were below the lower limit of quantitation (0.8 ng/g) for both formulations. All adverse events reported were mild except for increased serum transaminases in one participant, which was moderate and not considered treatment related. In conclusion, there were no significant differences in bimatoprost concentration between Formulations A and B in the epidermis/dermis layer of the scalp samples from the same study participants, with levels above efficacious concentrations. Treatment with bimatoprost 1% Formulations A and B was well tolerated.