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Successful therapy for chronic diseases affecting the posterior segment of the eye requires sustained drug concentrations at the site of action for extended periods of time. To achieve this, it is necessary to use high systemic doses or frequent intraocular injections, both associated with serious adverse effects. In order to avoid these complications and improve patient's quality of life, an experimental study has been conducted on the preparation of a new generation of biodegradable poly(D,L-lactide-co-glycolide) (50:50) (PLGA) polymer microspheres (MSs) loaded with Dxm, vitamin E and/or human serum albumin (HSA). Particles were prepared according to a S/O/W encapsulation method and the 20-40μm fraction was selected. This narrow size distribution is suitable for minimally invasive intravitreal injection by small calibre needles. Characterisation of the MSs showed high Dxm loading and encapsulation efficiency (> 90%) without a strong interaction with the polymer matrix, as revealed by DSC analysis. MSs drug release studies indicated a small burst effect (lower than 5%) during the first five hours and subsequently, drug release was sustained for at least 30days, led by diffusion and erosion mechanisms. Dxm release rate was modulated when solid state HSA was incorporated into MSs formulation. SDS-PAGE analysis showed that the protein maintained its integrity during the encapsulation process, as well as for the release study. MSs presented good tolerance and lack of cytotoxicity in macrophages and HeLa cultured cells. After 12months of storage under standard refrigerated conditions (4±1°C), MSs retained appropriate physical and chemical properties and analogous drug release kinetics. Therefore, we conclude that these microspheres are promising pharmaceutical systems for intraocular administration, allowing controlled release of the drug., (Copyright © 2016 Elsevier B.V. All rights reserved.)

Ocular drug delivery is one of the most fascinating and challenging tasks facing pharmaceutical researchers. Improving drug ocular residence time and/or penetration is complex. Microparticles (MP) provide interesting opportunities to increase ocular bioavailability of drugs and patient compliance brought about by decreased frequency of dosing. However, sustained-release microsphere formulation would fail to accomplish the task of long-lasting drug release unless microspheres remained for a prolonged period at the site of action. Some strategies have been assessed to retain MP at the target site. Among them, improving bioadhesion properties is possibly the one that offers the best technical features to date. In this review, we present the latest scientific communications in the field of MP development and coating to increase bioavailability when MP are destined for ocular treatment. All of these are more or less useful tools that must be considered as an important part of the development process for ocular medication optimization. [ABSTRACT FROM AUTHOR]