Impact of altered hydrophobicity and reduced agglomeration on dissolution of micronized poorly water-soluble drug powders after dry coating.

The impact of dry coating with hydrophobic or hydrophilic nano-silica at 25-100% surface area coverage on dissolution of micronized poorly water-soluble drugs was investigated by examining their agglomeration and surface hydrophobicity. Ibuprofen (20 µm and 10 µm) and griseofulvin (10 µm) were selected having differing solubility, hydrophobicity, and surface morphology. Characterization involved particle agglomeration via two dry dispersion methods, drug dissolution using the USP IV method, cohesion reduction through shear testing, and powder wettability via the modified Washburn method. Dry coating dramatically reduced the cohesion hence agglomerate size of both the coated ibuprofen particles, but less for griseofulvin, attributed to its surface morphology. For hydrophobic silica, agglomerate size reduction outweighed the adverse impact of increased surface hydrophobicity for ibuprofen. For griseofulvin, the agglomerate reduction was much lower, not able to overcome the effect of increased drug particle hydrophobicity with hydrophobic silica coating. Hydrophilic silica coating reduced hydrophobicity for all three drug powders, leading to the synergistic improvement in the dissolution along with agglomerate size reduction. Overall, the combined effect of the drug particle surface hydrophobicity and agglomerate size, represented by specific surface area, could explain the dissolution behavior of these poorly water-soluble drugs.