Sustained release formulations of a potent antithrombotic drug, cilostazol, in poly-(lactic acid-co-glycolic acid) (PLGA) matrices were created for luminal release from a novel drug-eluting stent utilizing reservoirs (RES TECHNOLOGY™). The crystallinity of cilostazol and the morphology of the cilostazol/polymer matrix in the stent reservoirs were examined by cross-polarized optical microscopy and differential scanning calorimetry. An in vitro method was developed to study release kinetics of various cilostazol formulations and to examine correlation with in vivo release. Formulation parameters such as drug-to-polymer ratio and the use of a polymer barrier on the abluminal surface of the drug/polymer matrix were found to be effective in modulating drug release rate. Cilostazol/PLGA(75/25) in the weight ratio of 50/50 to 70/30 displayed first-order release kinetics for the majority of the drug load. Addition of an abluminal polymer barrier slowed cilostazol release rate when compared to the bidirectional reservoir design. Excellent correlation between cilostazol in vivo release profile from stents in a porcine coronary artery model and that measured in vitro in a modified USP-7 apparatus suggests that the in vitro release system is capable of predicting in vivo release of cilostazol from stent reservoirs.
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