Kinetic analysis of chlorpropamide dissolution from solid dispersions

Solid dispersions (SDs) of chlorpropamide were prepared by the solvent deposition technique using two grades of microcrystalline cellulose as carrier materials with different ratios of drug to carrier. The dissolution rate of chlorpropmide from the SDs was carried out at two physiological pH values of 1.1 and 7.25 simulating gastric and intestinal environments. The dissolution was dependent on the grade, the ratio of drug to carrier and pH. The higher dissolution was observed for more hydrophilic grade of the carrier as well as the higher ratio of carrier to drug. At the higher pH the drug dissolved much faster than the lower pH. X-ray diffraction showed some reduced drug crystallinity in SDs whereas infrared spectroscopy revealed no drug interactions with solvent and the carriers. The enhanced dissolution was attributed to the reduced drug crystallinity, decreased particle size, increased wettability and reduced aggregation of the hydrophobic drug particles. A novel model denoted as reciprocal powered time model with its theoretical justification was employed to analyze the dissolution data and proved to be superior to commonly used models for the analysis of the data. There was a quantitative relation between the model parameter and the ratio of carrier to drug which could be of value in dissolution rate prediction.