Formation of mannitol core microparticles for sustained release with lipid coating in a mini fluid bed system
The goal of this study was to prepare sustained release microparticles for methyl blue and aspartame as sparingly and freely water-soluble model drugs by lipid film coating in a Mini-Glatt fluid bed, and to assess the effect of coating load of two of lipids, hard fat and glyceryl stearate, on the release rates. 30 g drug-loaded mannitol carrier microparticles with average diameter of 500 or 300 μm were coated with 5 g, 10 g, 20 g and 30 g lipids, respectively. The model drugs were completely released in vitro through pores which mainly resulted from dissolution of the polyol core beads. The release of methyl blue from microparticles based on 500 μm carrier beads extended up to 25 days, while aspartame release from microparticles formed from 300 μm carrier beads was extended to 7 days. Although glyceryl stearate exhibits higher wettability, burst and release rates were similar for the two lipid materials. Polymorphic transformation of the hart fat was observed upon release. The lipid-coated microparticles produced with 500 μm carrier beads showed slightly lower burst release compared to the microparticles produced with 300 μm carrier beads as they carried relatively thicker lipid layer based on an equivalent lipid to mannitol ratio. Aspartame microparticles showed a much faster release than methyl blue due to the higher water-solubility of aspartame.