Plasma Protein Binding

The binding of drug to plasma proteins is a major determinant of drug disposition & distribution and plays an important role in modulating pharmacodynamic effects since in most cases only the free (unbound) drug is responsible for the pharmacological activity.

In most cases, plasma protein binding (PPB) is measured using undiluted human or animal plasma. In some cases, a semi-mechanistic investigation of the roles of certain plasma proteins may offer some insights in understanding compound PK profiles. The proteins commonly involved in binding with drugs are albumin, lipoproteins, and alpha-1-acid glycoprotein (AAG or AGP).

Acidic and neutral compounds generally tend to interact with albumin, while basic substances may prefer binding to the acidic AAG molecule. QDI has done detailed binding characterizations of compounds to AAG and human serum albumin (HSA).

Assay Methodology

QDI has various assay formats to measure PPB, including Rapid Equilibrium Dialysis (RED), ultrafiltration and ultracentrifugation. Generally PPB experiments are performed using the RED format in a 48-well format. Sometimes for highly bound compounds, the ultracentrifugation method is performed. For compounds not stable in plasma, a quick ultrafiltration assay can be performed in minutes rather than hours.

Plasma Protein Binding: Standard Assay Conditions (Customizable)

Testing Compound Concentration
1 μM

Dialysis buffer
PBS, pH 7.4

Incubation Period
4 hour at 37 °C, 10% CO2 if needed

Detection Method

Control Compound

Human, rat, mouse, dog and monkey (additional species are available on request)

% Bound

Turnaround Time
2-3 Days

Compound requirements
20 μL 10 mM DMSO stock