Abstract
The binding of some pyrazolone and pyrazolidine derivatives to bovine serum albumin was investigated by a dynamic dialysis method. The drugs used were aminopyrine, antipyrine, 4-aminoantipyrine, phenylbutazone, and oxyphenbutazone. Analysis of the binding data indicated that albumin possesses a single strong binding site and secondary classes of several sites with a much lower affinity for the drugs examined and the values for the association constant of the pyrazolidine derivatives are much greater than that of the pyrazolone derivatives. The affinity of binding is also shown to depend on the hydrophobic character of each drug, as expressed by a partition coefficient. The thermodynamic parameters indicated that these interactions are exothermic and occur spontaneously under the experimental conditions used. It is possible that the pyrazolone derivatives compete with pyrazolidine derivatives for plasma protein binding. However, the extended calculation for the whole body indicates that the plasma protein binding of pyrazolone and pyrazolidine derivatives probably play only a minor role in clinical medication.
