Solubilization and interaction of sulindac with polyvinylpyrrolidone K30 in the solid state and in aqueous solution

In this report the interactions of sulindac with polyvinylpyrrolidone K30 (PVP K30), both in the solid state and in aqueous solution, have been investigated. Solid dispersions of sulindac with PVP K30 were prepared by the solvent method in ethanol from various drug-to-polymer weight ratios. X-ray powder diffraction and differential scanning calorimetry have shown that PVP inhibits the crystallization of sulindac. The stabilization of the noncrystalline state of sulindac was shown by x-ray diffractometry after a 1-year storage. There was a considerable increase in the release rate of the drug when the polymer content was increased and the intrinsic dissolution rate values of these systems were calculated. From the UV spectra a bathochromic shift and a well-defined isosbestic point were observed at pH 2 and 6, which confirmed an interaction between the drug and the polymer in solution. Moreover, the apparent solubility of sulindac has been modified as a function of the polymer concentrations. The binding process between the drug and PVP was exothermic from the stability constant values at 25, 30, and 37 degrees C at pH 2.