Polymeric micelles for oral drug delivery

In the case of chronic therapies, the oral route is often the preferred route for drug administration given its acceptability and convenience. However, various factors which limit drug absorption through the gastro-intestinal (GI) mucosa contribute to restricting the bioavailability of the drug, that is, the actual amount which reaches the bloodstream. Among these factors, poor drug permeability through the GI mucosa and/or low aqueous solubility are of central importance. Polymeric micelles, which form upon self-assembly of amphiphilic macromolecules, can act as vehicles for the oral delivery of these drugs. This manuscript summarizes the literature in relation to the design of these micellar systems and their characterization with respect to drug loading and retention properties as well as the ability to withstand dissociation and drug discharge upon oral administration. Also, the role of certain polymers in improving drug absorption through the GI mucosa, either by increasing membrane permeability to the drug and/or carrier or by inhibiting drug efflux transporters in the GI mucosa, is discussed. Finally, this review reports other drug delivery strategies such as using bioadhesive polymers which may lengthen residence time in the GI tract and promote drug permeation, or rendering the polymeric micelles pH-sensitive in order to ensure drug release from the carrier at its site of absorption.