We designed ophthalmic formulations containing dexamethasone-loaded solid nanoparticles (DEXnano dispersion), and investigated corneal permeability and toxicity. 0.1% dexamethasone (DEX) powder (DEX microparticles), 0.026% methyl p-hydroxybenzoate (MP), 0.014% propyl p-hydroxybenzoate (PP), and 0.5% methylcellulose were used, and the DEXnano dispersion was prepared by the bead mill method. The mean particle size of DEXnano dispersion was 78 nm. Antimicrobial activity of the DEXnano dispersion were measured by using Escherichia coli, and the corneal epithelium-debrided rat model and HCE-T cells (immortalized human corneal epithelial cell line) were used to estimate the corneal toxicity. The transcorneal penetration of the DEXnano dispersion were evaluated in the corneas of rabbit. The DEXnano dispersion was found to be highly stable until 14 d after its preparation. Although DEX itself did not exhibit antimicrobial activity, the DEXnano dispersion containing parabens (MP and PP) showed high antimicrobial activity, approximately equal to that of the solution containing parabens without DEX. The corneal penetration rate (Jc) and mean residence time (MRT) of DEX from the DEXnano dispersion were approximately 5.1- and 1.3-fold higher, respectively, than those of a dispersion containing DEX microparticles (mean particle size, 11.3 µm). In addition, no significant difference was found in corneal stimulation between the vehicle and DEXnano dispersion. In conclusion, we successfully prepared high quality dispersion containing DEX solid nanoparticles, and the nanoparticle-based ophthalmic formulation of DEX enhanced the corneal permeability and residence time of the drug. It is possible that DEXnano dispersion will show increased effectiveness in treating ocular inflammation.
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