Solubilization and interaction of sulindac with beta-cyclodextrin in the solid state and in aqueous solution

A sulindac-beta-cyclodextrin complex was obtained by the coprecipitation method. Kneaded solids and physical mixtures were also prepared. The complex was shown by x-ray powder diffraction to be noncrystalline whereas pure drug and any of the other sulindac-beta-CD system were crystalline. the endothermic peak of sulindac due to the fusion of drug disappeared in DSC thermograms for the coprecipitate product, which confirmed the interaction between sulindac and beta-CD in the solid state. After a 1-year storage drug crystals could not be observed by x-ray diffractometry, which indicated that the complex formed was stable. The complex showed the fastest dissolution rate which might be attributed to the high-energy noncrystalline state and the inclusion complex formation in solution. UV spectra were modified and the apparent solubility of the drug increased with the addition of beta-CD, which confirmed the interaction between sulindac and the ligand in solution. The apparent stability constant, K1:1, for the complex at pH 2 and 25, 30, and 37 degrees C was 340, 220, and 160 M-1, respectively, which confirmed the influence of temperature on the complex stability. The value of K1:1 at pH 6 and 25 degrees C was 139 M-1, which indicated that the complex is formed easier with the non-ionized sulindac. The enthalpy change, delta H degree, showed that the binding process is exothermic.