Physiologic considerations in drug absorption from the gastrointestinal tract.

The dynamic interaction between variables within the gastrointestinal tract and the physiochemical properties of a drug in a delivery system determine the rate and extent of absorption of that drug. Among the major physiologic variables are pH, gastric emptying time, and intestinal transit time. Some physicochemical properties of interest include solubility, particle size, and chemical form of the drug. Attributes of the formulation such as controlled-release mechanism, pH sensitivity, and size, shape, and density of the product can also affect absorption. Food has also been reported to influence the absorption from some but not all controlled-release products. As a more thorough understanding of the many factors involved in drug absorption is developed, the formulation of more sophisticated oral drug delivery systems will be possible.