A cationic nanocrystal formulation containing dexamethasone acetate nanocrystals (0.05%) and polymyxin B (0.10%) for ophthalmic application was produced using a self-developed small scale method for wet bead milling. The formulation developed offers the advantage of increased saturation solubility of the drug (due to the nano-size of the crystals), increased residence time in the eye (due to small size and increased mucoadhesion by the cationic charge) resulting ultimately in potential increased bioavailability. Characterization of the nanosuspensions by photon correlation spectroscopy (PCS) and transmission electron microscopy showed that the production method was successful in achieving dexamethasone crystals in the range of about 200-250 nm. The physical stabilization of the nanocrystals and generation of the positive charge was realized by using cetylpyridinium chloride (CPC) and benzalkonium chloride (BAC) at the concentration of 0.01%. In contrast to other cationic excipients, they are regulatorily accepted due to their use as preservatives. 

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