The effects of water-soluble polymers on cyclodextrins and cyclodextrin solubilization of drugs

For a variety of reasons, including cost, formulation bulk and toxicology, the amounts of cyclodextrin (CD) that can be included in drug formulations is limited. This is further complicated by the fact that the complexation efficacy of CDs is, in general, very low and their molecular weight is rather high. Here we review studies which have shown that complexation efficacy of CDs can be significantly enhanced by including a small amount of water-soluble polymer in the aqueous complexation medium. The polymers increase the apparent stability constant of the drug/CD complexes through formation of ternary drug/CD/polymer complexes. Thus, in average 40 to 50% less CD is needed when a polymer is present. Furthermore, some studies have shown that drug bioavailability from formulations containing a ternary drug/CD/polymer complex is greater than from a comparable drug/CD binary complex. In general, the water-soluble polymers improve both pharmaceutical and biological properties of drug/CD complexes.