ABSTRACT
Oral drug delivery remains the preferred route of delivery of therapeutic agents predominantly because of the ease of administration and, hence, patient compliance (Lee et al., 1997). Development of oral dosage forms is complicated by physiological characteristics of the gastrointestinal tract and physical considerations for both the drug and the intestinal route (e.g., regional differences in pH, epithelial and luminal enzymes, transit time within the different segments of the intestine, dissolution rate of the drug, stability of the drug within the environment of the intestine, etc.) (Lee et al., 1997; Smith et al., 1998). In developing an oral dosage formulation, the drug delivery scientist must consider the variety of routes by which a compound can be transported by the intestine and the particular characteristics of the drug, including its physicochemical as well as its pharmacokinetic and pharmacodynamic properties (Smith et al., 1992; Lee et al., 1997). As can be seen from Figure 31.1, transport of drugs across the intestinal epithelium can occur by a variety of mechanisms that exist either within the membranes of the epithelial cells (A, C, D, E, F) or by passive processes between the epithelia cells via the tight junctions (TJs) (B).
