This article provides an overview of mechanism of the drug absorption from the GI tract based on solubility/dissolution and dissociation/pH characteristics of a drug. It is argued that although pH values of the environment (stomach and intestine) may play a role, it is the availability of the large surface area of the intestine which predominantly is responsible for the drug absorption for both acidic and basic drugs. Furthermore, in the GI tract drugs exist in three forms i.e. solid (outside solvent/solution) and solid and ions in solution which are in equilibrium with one another. However, it is only the drug in solution form which is relevant for the absorption purpose. The roles of the interactions between drug (solid), drug/ions in solution and the surface areas are discussed in providing efficient drug absorption. Considering the absorption mechanism, the role of in vitro drug dissolution testing is also highlighted.Please click here for complete article
