Microparticulates for Ophthalmic Drug Delivery

Microparticulates are drug-containing small polymeric particles (erodible, non-erodible or ion-exchange resins) that are suspended in a liquid carrier medium. Upon administration of particle suspension in the eye, the particles reside at the delivery site (cul-de-sac, sub conjunctiva or vitreous cavity) and the drug is released from the particles through diffusion, chemical reaction, polymer degradation, or ion-exchange mechanism. Several distinct approaches have been used to formulate drugs in microparticulate dosage form for intraocular and topical application. These include erodible microparticulates, swelling mucoadhesive particulates, pH responsive microparticulates, nanoparticles/latex systems, ion-exchange resins, etc. Injection of bioerodible microparticulates in the vitreous for treating infections of posterior segment and the release of acceptable levels of drug up to two weeks has been demonstrated. Both corneal and non-corneal routes of drug entry in the eye from topical instillations are postulated. The in vitro and in vivo studies have shown that this dosage form holds great promise for sustained drug release in the eye. However, several formulation challenges, including production of stable suspensions, uniform dose per unit volume, efficient drug entrapment, reproducible and large scale manufacturing, uniform particle size, etc., have to be addressed. Fruitful resolution of technological challenges will result in a superior dosage form for both topical and intraocular ophthalmic application. Recent developments and future challenges of microparticulate ophthalmic drug delivery system are discussed in this review.