Nile red nanosuspensions as investigative model to study the follicular targeting of drug nanocrystals.

The strategy of formulating poorly soluble actives as nanosuspension has been explored by more than a thousand research papers, with some medicinal products for oral and intravenous use having reached the market or advanced clinical trials. Interestingly, there is a limited number of reports of nanosuspensions formulated for dermal and transdermal drug delivery. In the present work, a nanocrystals suspension of the fluorescent, water-insoluble dye Nile Red, is prepared through a media milling technique and exploited to characterize the fate of the nanosuspended drug when applied on the skin. More in detail, the accumulation of Nile Red nanocrystals inside the hair follicles is evidenced by scanning electron microscopy, and the diffusion of drug molecules in the different skin layers is evaluated by confocal microscopy and skin permeation studies. Overall, the combination of the analytical techniques provide a description of the mechanisms underlying dermal accumulation, and transdermal penetration of a drug formulated as a nanosuspension.