DETERMINATION OF PROTEIN-BINDING BY IN-VITRO CHARCOAL ADSORPTION

Certain compounds such as SC-52151 have extensive nonspecific adsorpti on to the ultrafiltration devices or to dialysis membranes and therefo re can not be measured by the conventional ultrafiltration or equilibr ium dialysis methods. A nets method based on charcoal adsorption was d eveloped to overcome this difficulty. Unlike many conventional methods . which are based on the separation of free drug from bound drug under equilibrium conditions, the new method is operated under nonequilibri um conditions ann involves measuring the time course of decline of the percentage of bound drug remaining in plasma while the free drug is b eing removed by charcoal adsorption. Theoretical aspects of the method and the data processing procedure are presented. SC-98A, a compound w ith minimal nonspecific adsorption to the ultrafiltration membrane, wa s used to demonstrate the applicability of this method against the ult rafiltration method. Using this method tire protein binding of SC-5215 1 in human plasma at 1.0 mu g/ml was determined to be in the range of 91.4-97.7% at room temperature.