Regional Variability in Intestinal Drug Absorption

rug delivery systems are becoming increasingly sophis-ticated as pharmaceutical scientists acquire a better un-derstanding of the physicochemical and biological parameters pertinent to their performance. Despite tremendous advancements in drug delivery, the oral route re-mains the preferred route for the administration of therapeu-tic agents because the low cost of therapy and ease of adminis-tration lead to high levels of patient compliance. The extensive advancements in genomics and combinatorial chemistry have led to the synthesis of many potential drug candidates, remov-ing the bottleneck in the drug discovery process. On the other hand, this high-throughput screening process has done little to address the issue of poor bioavailability (BA) of orally admin-istered drug candidates. Conventional oral dosage forms provide a specific drug con-centration in systemic circulation without offering any control over drug delivery. Controlled-release drug delivery systems (CRDDS) provide drug release at a predetermined, predictable, and controlled rate (1,2). An important requisite for the suc-cessful performance of oral CRDDS is that the drug should have good absorption throughout the gastrointestinal tract (GIT), preferably by passive diffusion, to ensure continuous absorp-tion of the released drug (3). The average time required for a dosage unit to traverse the GIT is 3–4 h, although slight varia-tions exist among various dosage forms (see Table I)