Relation between Membrane Transport and Transport within Body Fluid on the Expression of Pharmacological Activities of Drugs - Mass Transfer in the Quantitative Structure-activity Relationship (QSAR) -

The activities of drugs are attributed to both the transport process from the intake-region to the organ where the drugs act and the action process at the objective organ. It is generally recognized that the transport process depends on the hydrophobicity of the drugs, and that the action process is affected by their structure. Usually, there is a linear relationship between the rate constant of the transport process (permeability coefficient) and the activity of the drug. However, it has been frequently reported that the drug activity is inversely proportional to the drug hydrophobicity, when the drug hydrophobicity is too strong. By assuming keeping of the steady-state transport of the drugs, a parabolic relationship between the activity of drugs and the hydrophobicity of drugs can be proved by considering both the permeability coefficient of drugs within the membrane and that within the body fluid. Since there are many ionic drugs, we explain the ion-transport mechanism based on the electroneutrality and the interfacial potential formed based on the distribution of both the objective ion and the counter ion. In addition, the ion transport across the bilayer lipid membrane caused by application of the membrane potential is interpreted.