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

Abstract

The purpose of this study was to investigate the effects of both water-soluble polymers and various drugs on the solubility of β-cyclodextrin ( βCD) in aqueous solution. The solubility of βCD 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°C for 20–40 min) increased the solubility to 21 mg/ml. The aqueous solubility of βCD also increased upon drug– βCD complex formation. Both lipophilic and hydrophilic drugs increased the solubility of βCD in water. For example, the solubility of βCD 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 βCD in such aqueous systems appeared to be the sum of the intrinsic solubility of βCD and the solubility of the various βCD complexes, i.e. the drug– βCD complexes and the complexes of βCD and drug– βCD complexes with the water-soluble polymers. Not only did the polymer solubilize βCD and its complexes, but was also able to enhance drug– βCD complex formation.