The effect of water-soluble polymers on the aqueous solubility and complexing abilities of β-cyclodextrin

The purpose of this study was to investigate the effects of both water-soluble polymers and various drugs on the solubility of beta-cyclodextrin (beta CD) in aqueous solution. The solubility of beta CD in water was determined to be 18.6 mg/ml, but addition of 0.25-1.00% (w/v) of polyvinylpyrrolidone, and heating in an autoclave (120-140 degrees C for 20-40 min) increased the solubility to 21 mg/ml. The aqueous solubility of beta CD also increased upon drug-beta CD complex formation. Both lipophilic and hydrophilic drugs increased the solubility of beta CD in water. For example, the solubility of beta CD in a saturated aqueous solution of carbamazepine was determined to be 28.4 mg/ml but 53.3 mg/ml when 0.25% (w/v) hydroxypropyl methylcellulose (HPMC) was present in the solutions. The total solubility of beta CD in such aqueous systems appeared to be the sum of the intrinsic solubility of beta CD and the solubility of the various beta CD complexes, i.e. the drug-beta CD complexes and the complexes of beta CD and drug-beta CD complexes with the water-soluble polymers. Not only did the polymer solubilize beta CD and its complexes, but was also able to enhance drug-beta CD complex formation. (C) 1998 Elsevier Science B.V. All rights reserved.