Factors Affecting Adhesion of Drug Particles to Surfaces in Pharmaceutical Systems
The mechanism of adhesion of drug powders on the surface of polymer coated glass beads was studied. Glass beads (500 µm) were air suspension coated using a 5% hydroxypropylmethylcellulose phthalate solution in dichloromethane: methanol solvent (50:50). Specific particle size fractions of several sulphonamide powders were prepared by fluid energy milling and sonic sifting; distributions were characterized by laser diffraction. Average charge to mass ratios on particle detachment were measured using an air stream Faraday cage. Total adhesion was determined by a centrifugal method and characterized by an S50 value, i.e. the speed required to detach 50% of the drug particles. Electrical interactions probably caused by triboelectrification during the preparation of the interactive system contributed significantly to the initial drug adhesion. Adhesion decreased with time and was well correlated with the charge to mass ratio decrease. The rate of decrease in adhesion increased with increasing relative humidity. Adhesion did not occur uniformly over the polymer surface with local multilayer adsorption occurring when the drug concentration was increased. When the interactive systems were prepared at higher relative humidity conditions (60% RH), adhesion between the drug particles and surface was significantly decreased; non-electrical interactions contributed to the adhesion process under these conditions.
KeywordsLiquid Bridge Drug Particle Average Charge Particle Layer Carrier Surface
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