ABSTRACT
The most preferred route for delivering therapeutic agents is oral drug delivery. However, this route is not feasible for delivery of hydrophilic macromolecules, such as therapeutic peptides, proteins, nucleotides, and efux pump substrates, because of negligible oral bioavailability. This is because of the barriers confronted by these molecules along the oral route, such as diffusion barrier of mucus, enzymatic barrier of peptidases, and permeability barrier of membranes. The strategies to surmount these barriers are by utilization of permeation enhancers, enzyme inhibitors, and multifunctional polymers, ideally guaranteeing both permeation enhancement and enzyme inhibition. In case of multifunctional polymers, these effects can take place only if polymers offer strong mucoadhesive features for providing a tight contact with the mucosa during the whole period of peptide drug release and absorption. Among the group of multifunctional polymers exhibiting all of the aforementioned properties, thiolated polymers (designated thiomers) are the most promising. The thiomers are hydrophilic macromolecules exhibiting free thiol groups on the polymeric backbone as poly(acrylates), carboxymethyl cellulose, alginate, pectin, deacetylated gellan gum, or chitosans.
6.1 Introduction .......................................................................................................................... 121 6.2 Synthesis of Thiolated Chitosan ........................................................................................... 122 6.3 Determination of Thiol Group .............................................................................................. 126 6.4 Properties .............................................................................................................................. 127
