ABSTRACT
In the last decade lipids have gained remarkable interest as potential carrier to deliver new drug molecules with enhanced bioavailability mostly exhibiting poor aqueous solubility. The success of lipids as drug carriers has been reflected in a number of lipid based formulations, which are clinically available or are currently undergoing clinical trials. Lipid based drug delivery systems range from simple solutions of drugs in oil to more complex mixtures of drugs dissolved in lipids, surfactants, cosurfactants and cosolvents. The delivery systems most often rely on presentation of the active substance in a solubilized form to enhance bioavailability. If by any chance the drug precipitates, the advantage of this technique is nullified. Lipid based nanocarriers include mixed micelles, liposomes, nanostructured lipid carriers, emulsion, microemulsions, nanoemulsions, and self-(micro, nano) emulsifying drug delivery system (SEDDS/SMEDDS/SNEDDS). This strategy relies on the premise that drugs need to be in solution for adequate stability and gastrointestinal absorption. This system has led over the past years to successful bioavailability enhancement with the immunosuppressive agent cyclosporine A (originally marketed as ‘Sandimmune’ and now as the improved product Neoral®), and for the three HIV protease inhibitors (Norvir®), saquinavir (Fortovase®) and Amprenavir (Agenarase®). As many drugs are successfully marketed as lipid based formulations, the lipid based drug delivery system has a wide scope in terms of solubility and bioavailability enhancement. However, a few limitations of this delivery system such as the stability, classifications, the lack of validated database considering the solubility of drugs in lipids, manufacturing technique, indicate that development of successful regulatory guidelines still need to be addressed in depth to advance understanding of key criteria dictating the performance of technology.