The influence of increasing albumin concentrations on the determination of the binding of sulfamethoxy-pyridazine to human and bovine serum albumin.

The binding of sulfamethoxypyridazine to human and bovine serum albumin was determined at eight constant molar drug/albumin ratios for seven different albumin concentrations ranging from 0.1% to 1.5%. The serum albumin concentration affects the determination of the albumin binding of the drug in two different ways. 1. The relative affinity of the albumins for the drug increases with increasing albumin concentrations, while the numbers of binding sites remain constant. 2. The association constants taken from Scatchard plots decrease with increasing albumin concentrations. It is concluded that a direct comparison of binding constants obtained with different albumin concentrations, as widely done, can lead to misinterpretations and should be avoided.