Drug delivery systems: Smart drug delivery systems

Polymers have been indispensable in preparing various controlled release formulations. Of the many routes of drug administration, oral delivery is most attractive due to high patient convenience and compliance, but it is oft en very challenging. For example, oral delivery of drugs that are poorly soluble, or are not stable in the gastrointestinal tract, or have high molecular weights has been difficult. Delivery of high molecular weight drugs, such as peptide and protein drugs and oligonucleotides, by parenteral administration has also been difficult due to their short circulation half-lives as well as lack of suitable delivery systems for long-term delivery. A number of approaches have been explored to increase the bioavailability of hydrophilic/hydrophobic drugs, peptides, and proteins by conjugating drugs with natural or synthetic macromolecules or loading in polymeric drug delivery systems. Polymers with functional properties have been used to overcome hurdles in delivery of diverse drugs.