Abstract
The physicochemical characteristics and oral absorption of a poorly water-soluble drug, K-832, adsorbed onto porous silica (Sylysia 350), were compared with those of K-832 adsorbed onto non-porous silica (Aerosil 200). K-832 and silica were treated with supercritical CO2 (scCO2) to produce K-832-Sylysia 350 and K-832-Aerosil 200 formulations. Scanning electron microscopy, polarizing microscopy, powder X-ray diffraction, and differential scanning calorimetry results suggested that K-832 mainly existed in an amorphous state in both formulations. The specific surface area of both formulations was much larger than that of pure K-832 crystals. The dissolution rate of K-832 from both formulations was considerably greater than that from corresponding physical mixtures due to rapid wetting of the hydrophilic carrier surfaces and amorphous state, the dissolution from the K-832-Sylysia 350 formulation being the fastest. In vivo absorption tests on the two formulations indicated no significant differences in their peak concentration (Cmax) and the area under their plasma concentration–time curve (AUC), while the concentrations of K-832 in the K-832-Sylysia 350 formulation were significantly higher than those in the K-832-Aerosil 200 formulation 1 h and 1.5 h after administration of these formulations (p<0.05). This could be attributed to the different dispersion states of K-832 in the formulations due to their different three-dimensional structures (porous and non-porous). In physical stability tests, the amorphous drugs in both formulations were stable at room temperature for at least 14 months. Thus, the absorption of poorly water-soluble drugs could be greatly improved by adsorption onto porous silica using scCO2.
