Association and transfer functions for analysis of drug binding to proteins.

A global association function is proposed that characterizes the apparent overall equilibrium of drug protein binding. It is defined as a function of the total drug concentration and may be directly calculated from each experimental result. The binding transfer function represents the relative rates of change in the bound and free concentrations from the total concentration. Two applications are presented: one is an investigation of the effect of temperature on binding of salicylic acid to proteins in plasma; and the other is a comparison of the phenomenon in two different biological fluids (protein binding of sodium salicylate in plasma and in synovial fluid).