Cyclodextrin conjugates for colon drug delivery

Drug delivery to colon is beneficial for both local and systemic drug delivery and also for chronotheapeutic drugs. However, colon drug delivery is difficult due to its distal location in the gastrointestinal (GI) tract. Among different approaches used for colon drug delivery after oral administration, cyclodextrin (CD) conjugates utilizing CD covalent linkage with the drug is a promising approach due to its chemical and physical stability, solubility and biocompatibility. The main strategy to target cyclodextrin drug conjugates to colon is through ester bond formation between carboxylic group of the drug and hydroxyl groups of CDs. Due to this inherent limitation, only drugs with carboxylic groups could be combined with CDs. However, as a result of rapid progress in phytochemistry and biotechnology, many polyphenolic compounds, proteins and peptides containing carboxylic groups have been emerged as important therapeutic targets. These molecules suffer from poor solubility, stability and bioavailability in GI tract. Therefore, with these molecules, CD conjugation could be successfully utilized. This review discusses strategies to prepare CD conjugates, mechanism of drug release from CD conjugates, and published work on CD drug conjugates utilized in colon targeting.