Paraffin wax is potentially useful for producing spray-congealed drug-loaded\nmicroparticles with sustained-release and taste-masking properties. To date, there is little information\nabout the effects of blending lipids with paraffin wax on the melt viscosity. In addition, drug\nparticles may not be entirely coated by the paraffin wax matrix. In this study, drug-loaded paraffin\nwax microparticles were produced by spray-congealing, and the effects of lipid additives on the\nmicroparticle production were investigated. The influence of lipid additives (stearic acid, cetyl alcohol,\nor cetyl esters) and drug (paracetamol) on the rheological properties of paraffin wax were elucidated.\nFourier transform-infrared spectroscopy was conducted to investigate the interactions between the\nblend constituents. Selected formulations were spray-congealed, and the microparticles produced\nwere characterized for their size, drug content, degree of surface drug coating, and drug release.\nThe viscosity of wax-lipid blends was found to be mostly lower than the weighted viscosity when\ninteractions occurred between the blend constituents. Molten paraffin wax exhibited Newtonian\nflow, which was transformed to plastic flow by paracetamol and pseudoplastic flow by the lipid\nadditive. The viscosity was decreased with lipid added. Compared to plain wax, wax-lipid blends\nproduced smaller spray-congealed microparticles. Drug content remained high. Degree of surface\ndrug coating and drug release were also higher. The lipid additives altered the rheological properties\nand hydrophobicity of the melt and are useful for modifying the microparticle properties.
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