Nanocarrier systems for oral drug delivery: do we really need them?

In particular since the last two decades there is constantly increasing interest in nanocarrier systems. They are utilized in order to overcome the major challenges being associated with this route of administration - namely poor solubility (I), poor permeability (II) and poor GI-stability (III). In order to improve drug solubility nanonization of the API, the use of solid lipid nanoparticles and porous adsorbent particles have shown great potential. Nanocrystals and selfnanoemulsifying drug delivery systems (SNEDDS) resulted already in numerous marketed drug products. Moreover, proof-of-principle studies for nanocarrier systems providing enhanced oral drug uptake are available. By providing a comparatively more intimate contact with the absorption membrane, a prolonged GI-residence time and/or exhibiting permeation enhancing properties, oral absorption can be strongly improved. Likely because of safety considerations and because of insufficiently high bioavailability improvements (<5-fold), however, a commercial interest in these systems is limited. Poor GI-stability can be overcome by incorporating the drug in nanocarrier systems providing a protective effect towards an enzymatic attack in the GI-tract. Furthermore, as nanocarrier systems can at least to some extent diffuse into the mucus gel layer releasing their payload there, a presystemic metabolism of the drug on the way between the delivery system and the absorption membrane can be excluded. Future trends are mainly focusing on carrier systems capable of not just improving solubility but providing also controlled drug release as well as on nanocarrier systems capable of efficiently permeating the mucus gel layer without destroying it.