Preparation and Characterization of Pegaptanib Sustained Release Microsphere Formulations for Intraocular Application

Abstract

Purpose: : Macugen® (pegaptanib sodium injection) has been shown to be an effective pharmacotherapy –based treatment for age–related macular degeneration (AMD). Biodegradable microspheres facilitate the delivery of therapeutic agents in a controlled and sustained manner. The purpose of this investigation is to test the feasibility of a microsphere formulation for controlled and sustained intraocular delivery of pegaptanib.

Methods: : Pegaptanib was formulated in PLGA–based microspheres using a novel oil/water single emulsion solvent evaporation/extraction technique. The pegaptanib microsphere formulations were characterized for drug content (HPLC), morphology (SEM), and particle size (laser light scattering). In vitro release experiments were conducted in PBS (pH 7.4) containing 0.02% Tween–20 and 0.05% sodium azide. Stability and in vitro release profiles were quantified by HPLC assay. In vitro bioactivity was assayed by a cell–based gene expression assay. The in vivo performance was tested by intravitreous injection of pegaptanib microspheres using a 29 gauge syringe in New Zealand rabbits. Released pegaptanib was measured by an oligonucleotide–based hybridization assay.

Results: : The PLGA microsphere fabrication process provided well defined particles with smooth particle surface and monolithic internal morphology. Pegaptanib encapsulation efficiency was excellent (≥95%) and high drug loadings were achieved (12–15 wt %) within the polymer matrix. HPLC analysis of pegaptanib showed no degradation of API during the fabrication process. The in vitro release profiles illustrated a limited burst release (<10%) followed by polymer–controlled sustained release of several weeks. The bioactivity of pegaptanib collected at various time points during the course of PBS release was equivalent to pegaptanib positive control. The in vivo performance of one microsphere formulation characterized after intravitreous injection in New Zealand rabbits revealed sustained levels of pegaptanib over several weeks.

Conclusions: : PLGA–based microspheres represent a viable sustained release delivery system for pegaptanib based on API encapsulation, stability, release kinetics, bioactivity and sustained release in an animal ocular model.

Keywords: age-related macular degeneration • vitreous