Evaluation of host-guest complex formation between a benzimidazolic derivative and cyclodextrins by UV-VIS spectrophotometry and differential scanning calorimetry

Interactions between a benzimidazolic derivative, omeprazole (OME), beta-cyclodextrin (beta CD) and a chemically modified beta CD, methyl-beta-cyclodextrin (M beta CD) were investigated in aqueous solution by UV-VIS spectroscopy and in solid state by differential scanning calorimetry (DSC). Phase solubility studies were used to evaluate the complexation in aqueous solution. The two solubility diagrams obtained were A(L) type, indicating the formation of a drug-cyclodextrin complex with 1:1 stoichiometry. The complex of OME with M beta CD showed a higher stability constant (K (S)) than those with beta CD. Some evidences of inclusion complexation in solid state were obtained from DSC. Only in thermal curves of OME-beta CD lyophilized product and in OME-M beta CD spray-dried and lyophilized systems the melting point of the drug disappeared completely suggesting the possible formation of an inclusion complex.