Improvement of dissolution rate and stability in a pirenoxine ophthalmic suspension by the bead mill methods

Foreign matter sensation and blurred vision following instillation of ophthalmic suspension are often observed, and remaining of solid particle on cornea is related these side eŠects. In addition, low dispersion stability in the ophthalmic suspension aŠects the therapeutic eŠect. In this study, we have attempted to enhance the dissolution rate and stability of commercially available pirenoxine ophthalmic suspension (CA-pirenoxine eye drops), anti-cataract eye drops, by changes in particle size. Methylcellulose, zirconia beads (0.1 mm) and Micro Smash were used to mill the pirenoxine (bead mill method), and the distribution of particle size was changed to approximately 60-900 nm (nanodispersions) from 70 nm-3 μm (CA-pirenoxine eye drops). The dissolution rate of pirenoxine increased by the bead mill, and the dissolution rate constant in pirenoxine nanodispersions was 2.1-fold than that in CA-pirenoxine eye drops. Moreover, the dispersion stability in nanodispersions also significant higher in comparison with the CA-pirenoxine eye drops. The dispersion ratio in CA-pirenoxine eye drops and pirenoxine nanodispersions at 2 d after suspension was 48％, 99％, respectively. In conclusion, we showed that the dissolution rate and dispersion stability of CA-pirenoxine eye drops were enhanced by the bead mill method. These findings provide significant information that can be used in the design of ophthalmic suspension.