Microspheres and nanoparticles used in ocular delivery systems

Microparticles and nanoparticles are colloidal drug carriers in the micro- and submicron range. These systems were developed to overcome solubility problems of poorly soluble drugs as well as for long acting injectable depot formulations and specific drug targeting options. These carriers were also evaluated for ophthalmic drug delivery purposes over the past 15 years. The main objective for these systems was to improve the classical aqueous eye drop formulations which have major disadvantages like a rapid elimination of the drugs from the precorneal area. Consequently, colloidal carrier suspensions were designed to combine ophthalmic prolonged action with the ease of the application of liquid eye drops. The review summarizes the present manufacturing methods and the materials used for these delivery systems with respect to ophthalmic purposes. The distribution and penetration pathways of the particulate delivery systems are also described. The applications of drug-loaded particles are presented with focus on ophthalmic diseases like glaucoma, inflammations or infections of the eye. Accordingly, particulate carriers outlined in the review include systems loaded with pilocarpine, beta-blockers, hydrocortisone, amikacin, and miscellaneous drugs. Finally, the biodegradation and toxicity of the carrier materials under evaluation are reviewed.