To achieve effective drug concentration at the intended site for a sufficient period of time is a requisite desired for many drug formulations. For drugs intended to ocular delivery, its poor bioavailability is due to pre-corneal factors. Most ocular diseases are treated by topical drug application in the form of solution, suspension and ointment. However, such dosage forms are no longer sufficient to combat some ocular diseases. Intravitreal drug injection is the current therapy for disorders in posterior segment. The procedure is associated with a high risk of complications, particularly when frequent, repeated injections are required. Thus, sustained-release technologies are being proposed, and the benefits of using colloidal carriers in intravitreal injections are currently under investigation for posterior drug delivery. This review will discuss recent progress and specific development issues relating to colloidal drug delivery systems, such as liposomes, niosomes, nanoparticles, and microemulsions in ocular drug delivery.

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A simple, rapid, accurate and sensitive method was developed for quantitative analysis of dexamethasone acetate in microemulsions using high performance liquid chromatography (HPLC) with UV detection. The chromatography parameters were stainless steel Lichrospher 100 RP-18 column (250 mm x 4 mm i.d., 5 µm particle size), at 30 ± 2 ºC. The isocratic mobile phase was methanol:water (65:35; v/v) at a flow rate of at 1.0 mL.min -1. The determinations were performed using UV-Vis detector set at 239 nm. Samples were prepared with methanol and the volume injected was 20 µL. The analytical curve was linear (r 2 0.9995) over a wide concentration range (2.0-30.0 µg.mL -1 ). The presence of components of the microemulsion did not interfere in the results of the analysis. The method showed adequate precision, with a relative standard deviation (RSD) smaller than 3%. The accuracy was analyzed by adding a standard drug and good recovery values were obtained for all drug concentrations used. The HPLC method developed in this study showed specificity and selectivity with linearity in the working range and good precision and accuracy, making it very suitable for quantification of dexamethasone in microemulsions. The analytical procedure is reliable and offers advantages in terms of speed and low cost of reagents. Um método simples, rápido, preciso e sensível foi desenvolvido para a análise quantitativa de acetato de dexametasona em microemulsões usando cromatografia líquida de alta eficiência (CLAE). Os parâmetros cromatográficos foram: coluna cromatográfica Lichrospher 100 RP-18, (250 mm x 4 mm i.d., 5 µm partícula tamanho), com temperatura de coluna de 30 ± 2 ºC. A fase móvel foi composta de metanol: água (65:35; v/v) com fluxo isocrático de 1 mL.min -1 e volume de injeção de 20 µL. As determinações foram realizadas utilizando detector UV-Vis no comprimento de onda de 239 nm. A curva analítica mostrou-se linear (r 2 0,999) em uma ampla faixa de concentração (2,0-30,0 µg.mL -1 ). A presença de componentes da microemulsão não interferiu nos resultados da análise. O método mostrou precisão adequada, com desvio padrão relativo menor que 3%. A exatidão foi analisada pela adição de padrões do fármaco e valores de recuperação dentro dos limites recomendáveis foram obtidos para todas as concentrações estudadas. O método por CLAE mostrou especificidade e seletividade com linearidade dentro da faixa de concentração utilizada e precisão e exatidão que tornam o método adequado para a análise de dexametasona em microemulsões. O procedimento analítico é fidedigno e oferece vantagens em termos de velocidade e custo de reativos. Unitermos: Acetato de dexametasona/determinação. Microemulsões/análise quantitativa. Cromatografia líquida de alta eficiência/análise quantitativa. Método de análise/validação.

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