the use of diluent to reduce non - specific , drug binding provides a simple , flexible and biocompatible way to reduce chemical entity nsb so that bioassay results may more closely predict the behavior of these compounds in vitro . additionally , the use of diluent as the chemical entity diluent enhances the predictive nature of data emanating from high throughput drug assays such as caco - 2 drug transport assays , plasma protein drug binding assays , pampa assays , permeability assays , and drug solubility assays . the diluent is made by either filtering a selected plasma through an ultrafiltration membrane having nominal molecular weight cutoff of about 30 kd , preferably about 10 kd or below or by selectively adding individual components of a plasma or serum that do not contribute to non - specific binding .