Oral drug absorption is usually dependent on drug's physicochemical properties, formulation design and physiological conditions of gastrointestinal tract [1] . It is well known that physicochemical properties of drugs, like molecular weight, crystal structure, lipophilicity, pKa could generally determine the absorption mechanism [2]. Physiological conditions of gastrointestinal tract, i.e., expression level of drug metabolizing enzymes (polymorphism), empty/transit of GI tract, food effect, and

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... drug-drug interaction caused by induction or inhibition of metabolism all contributed to the rate and extent of oral drug absorption [3, 4] . In the last decade, progress on transporter studies showed increasingly significance of carriermediated absorption in drug development and clinical applications [5, 6] . With more understanding of drug transporters, many previous puzzles on clinical pharmacokinetics and drug-drug interaction could be well explained. Furthermore, targeting on transporters also provided unique strategy to improve drug absorption or overcome unfavorable absorption barrier. This editorial aimed to briefly outline the major transporters and their roles on oral drug absorption, especially to efflux transporters.