Poor solubility remains a major challenge for pharmaceutical industry, which is now considered to be an area of prime importance in the field of biomedical research. Approximately 40% new molecular entities (NMEs) synthesized in pharmaceutical R with advanced combinatorial chemistry and computer aided drug designing (CADD) approaches suffer from poor solubility and bioavailability related issues. Apart from these presence of intestinal tight junctional epithelial cells, transporters and enzymatic barriers further reduces the oral absorption of drugs. Implication of the novel lipid based nanocarriers and nanomaterials like dendrimers and carbon nanotubes as a delivery system can effectively enhance the oral bioavailability of drugs by breaching the barriers, and resolve all critics related to solubility and bioavailability. Thus prime objectives of this review are to give in-depth knowledge and critical appraisal on the barriers for poor oral bioavailability of drugs, along with various novel formulation approaches used for bioavailability enhancement such as lipid based formulations, nanosizing techniques, complexation with polymers and nanomaterials like dendrimers, carbon nanotubes, and penetration enhancers. Also it gives a brief account on in vitro, in vivo screening methods used for assessment of oral bioavailability, and regulatory considerations for the approval.
Keywords: Bioavailability, lipids, permeability, solubility, regulatory considerations, BCS, IVIVC, Colloidal carriers, Self-emulsifying drug delivery, Absorption barriers
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