P-glycoprotein inhibitors and their screening: a perspective from bioavailability enhancement.

Drug efflux pumps like P-glycoprotein (P-gp) and multidrug resistance (MDR) proteins were recognized to possess functional role in determining the pharmacokinetics of drugs administered by peroral as well as parenteral route. Advancements in molecular biology, to some extent, had revealed the structure, localization and functional role of P-glycoprotein and its mechanism of drug efflux. Broad substrate recognition by this protein and clinical implications of its inhibition has revolutionized cancer chemotherapy leading to design and development of novel P-glycoprotein inhibitors. In the recent times, the application of these inhibitors in improving peroral drug delivery has gained special interest. Inhibition of P-glycoprotein improves intestinal absorption and tissue distribution while reducing the substrate metabolism and its elimination. Eventually, various screening methodologies have been developed for determining the activity of P-glycoprotein, kinetics of drug transport and identification of substrates and inhibitors. In the present review, techniques used for screening P-glycoprotein inhibitors and the scope of these inhibitors in optimizing peroral drug absorption and pharmacokinetics are discussed along with a brief introduction to P-glycoprotein, its physiological function and active role in extrusion of drugs.