Oral dosage form is considered as the most convenient and commonly employed route of drug delivery due to the ease of administration, high patient compliance, cost-effectiveness, least constraints and flexibility in the design (Krishnaiah 2010). Drug companies have invested extensive effort on the development of oral drug products. However, although several factors can affect the bioavailability of an orally administrated dosage, e.g. first-pass metabolism, pre-systemic metabolism and susceptibility to efflux mechanisms, poor aqueous solubility and low permeability have been proven as the most frequent causes of low bioavailability (Sakaeda, Okamura et al. 2001; Vieth, Siegel et al. 2004).
by Qionghua Wei from Shaanxi, China 2016