Cyclodextrins and the Biopharmaceutics Classification System of Drugs

Although the biopharmaceutics classification system (BCS) was originally developed for solid oral dosage forms this system can be extended to other types of drug delivery forms. According to the BCS aqueous solubility and permeability are the most important parameters affecting drug bioavailability. Cyclodextrins can enhance the aqueous solubility of lipophilic drugs without changing their intrinsic ability to permeate biological membranes. Thus, through cyclodextrin complexation it is possible to move Class II drugs, and sometimes even Class IV drugs, into Class I. However, cyclodextrins can decrease bioavailability of Class I drugs and will in most cases not improve bioavailability of Class III drugs. Through formation of drug/cyclodextrin/polymer ternary complexes it is possible to enhance the complexation efficacy of cyclodextrins and at the same time improve drug bioavailability from cyclodextrin containing drug formulations.