The effect of bile salts and solvents on dissolution rate of phenytoin (PHT) from PHTpolyvinylpyrrolidone (PVP)-bile salts (1: 1: 1) solid dispersion (SD) prepared by a solvent removal method was investigated. Three kinds of bile salts, sodium deoxycholate, sodium cholate, and sodium lithocholate (LC-Na) were used. Methanol, ethanol, and n-propanol were employed as solvents. The dissolution rate of PHT from the PHT-PVP-LC-Na SD prepared with methanol was markedly increased among various SDs. Further, both X-ray diffraction measurement and infrared analysis were employed to confirm the estimation of the degree of PHT crystallization and for the characterization of interactions between PHT and additives such as PVP and/or bile salts as well.
Infrared spectra suggested an interaction, probably by hydrogen-bond formation, among PHT, PVP, and bile salts in SD. X-ray diffraction pattern of the powder indicated that PHT was amorphous in the PHT-PVP-LC-Na SD when methanol was used as a solvent. It was also revealed that the amorphous state of PHT in the SD attributed to the improvement of PHT dissolution property.