Mechanisms by which cyclodextrins modify drug release from polymeric drug delivery systems

For many drug candidates a modified in vivo drug release is desired to improve efficacy, sustain effect or minimise toxicity. Polymeric delivery systems, such as microspheres, nanospheres and polymeric films, have been extensively researched in an attempt to achieve modified drug release. Cyclodextrins offer an alternative approach. These cyclic oligosaccharides have the ability to form non-covalent complexes with a number of drugs and in so doing alter their physicochemical properties. In addition, the primary and secondary hydroxyl groups of the native (alpha, beta, gamma-) cyclodextrins are potential sites for chemical modification. It follows that the incorporation of these agents into polymeric drug delivery systems, as physical mixtures, covalently bound conjugates or cross-linking agents, frequently permits a greater degree of control of drug release. This paper reviews the incorporation of various cyclodextrins into polymeric formulations. The mechanisms by which cyclodextrin/polymer formulations act to modify drug release are considered.