A method of computing the distribution of a ligand among multiple binding sites on different proteins in plasma: thyroxine as an illustrative example.

This paper describes a computer program for estimating the amount of free or unbound ligand in the plasma as well as the distribution of the ligand among different sets of binding sites on different proteins. The input data consist of: the number and concentrations of proteins involved, the number of binding sites on each protein, the association constant and binding capacity of each set of sites for the ligand, and the total concentrations of ligand. The output provides tables of estimates of the concentration of free drug, the amount of ligand bound by each set of sites on each protein, the concentration of free protein, and the input values for reference. The distribution of thyroxine between thyroid binding globulin, prealbumin, human serum albumin and free drug is used as an illustrative example.