Plasma protein binding, cross-filtration

Only the free unbound fraction of a compound in blood circulation is able to diffuse or be transported through biological membranes, or to interact with receptors and enzymes. In order to make accurate in vivo predictions, it is important to evaluate the degree of binding of a study compound to plasma proteins. The degree of plasma protein binding is also an important parameter in PBPK modelling. The degree of plasma protein binding of study compounds are elucidated using rapid equilibrium dialysis (RED), ultrafiltration or cross filtration followed by analysis of the samples by LC/MS/MS. Also, TRANSIL high-sensitivity binding assay can be used to measure binding, if the binding is too high to be measured using the traditional methods or if the compound has high non-specific binding resulting in low recovery.