Purpose: Fingolimod (FTY720; FT), a structural analog of sphingosine, has potential ocular applications. The goal of this study was to develop an FT-loaded nanoemulsion (NE; FT-NE) formulation for the efficient and prolonged delivery of FT to the posterior segment of the eye through the topical route. Methods: FT-NE formulations were prepared using homogenization followed by the probe sonication method. The lead FT-NE formulations (0.15% and 0.3% w/v loading), comprising soybean oil as oil and Tween® 80 and Poloxamer 188 as surfactants, were further evaluated for in vitro release, surface morphology, filtration sterilization, and stability at refrigerated temperature. Ocular bioavailability following topical application of FT-NE (0.3%) was examined in Sprague-Dawley rats. Results: The formulation, at both dose levels, showed desirable physicochemical characteristics, a nearly spherical shape with homogenous nanometric size distribution, and was stable for 180 days (last time point checked) at refrigerated temperature postfiltration through a polyethersulfone (0.22 µm) membrane. In vitro release studies showed prolonged release over 24 h, compared with the control FT solution (FT-S). In vivo studies revealed that effective concentrations of FT were achieved in the vitreous humor and retina following topical application of FT-NE. Conclusions: The results from these studies demonstrate that the FT-NE formulation can serve as a viable platform for the ocular delivery of FT through the topical route.
Keywords: and physicochemical characterization; fingolimod; nanoemulsion; ocular drug delivery; stability; sterilization.