Plasma Protein Binding (PPB) Assays

Plasma Protein Binding Studies for Your Drug Candidate

Plasma protein binding is a quantification of the extent to which a drug attaches to proteins within the blood plasma. It is an important parameter to characterize the drug distribution process, as plasma protein binding may cause multiple effects, such as slowing down metabolism, reducing clearance, prolonging elimination half-life, and limiting drug distribution into target tissues. It is noteworthy that the concentration of the drug that remains unbound (free drug) at the therapeutic site is responsible for exerting the therapeutic effects.

As part of a full-scale preclinical program for drug discovery and development, plasma protein binding studies are of great significance in building the PK/PD models, predicting drug-drug interactions, evaluating drug toxicity, predicting human PK parameters and dosage regimens.

WuXi AppTec helps drug developers build ADME programs that include the right plasma protein binding assays and data-driven support needed to advance your compound from discovery to IND to NDA.

Accurate Plasma Protein Binding Testing

WuXi AppTec conducts more than 300,000 in vitro studies every year, with vast experience in plasma protein binding studies. With the support of WuXi AppTec’s comprehensive in vitro ADME service platform, you can get the quality data you need to optimize your compound and move into the next stages of development.

Plasma Protein Binding Assays

Plasma protein binding is often determined by various methods, including equilibrium dialysis, ultrafiltration, ultracentrifugation, flux dialysis, and more. The choice of method for plasma protein binding studies depends on various factors, including the specific drug properties, objectives of the study, and available resources. It is essential to carefully consider the strengths, limitations, and compatibility of each method with the drug under investigation to ensure reliable and valuable results.

Equilibrium dialysis
This method utilizes a semipermeable membrane to effectively separate the free and bound drug fractions. The semipermeable membrane selectively permits the passage of unbound drug molecules, while effectively retaining the protein-bound drug within the plasma compartment.

Ultrafiltration
Ultrafiltration is a technique used to distinguish and quantify the protein-bound and unbound drug fractions based on their varying molecular weights. This method involves passing the drug-containing sample through an ultrafiltration membrane with a specific molecular weight cutoff, allowing the smaller unbound drug molecules to pass through while retaining the larger protein-bound drug complexes.

Ultracentrifugation
Ultracentrifugation method uses an ultracentrifuge that operates at an extremely high speed, usually higher than 100,000 g, to separate free drugs from protein bound drugs in a tube that with no membrane. This method is useful for drugs that have problems with membrane effects, such as nonspecific binding and volume shifts.

Flux dialysis
The flux dialysis uses the same device as equilibrium dialysis to measure protein binding. It is based on the principle that the initial flux rate of a drug through a dialysis membrane is proportional to the product of the compound initial concentration, fraction unbound, and unbound dialysis membrane permeability. This method is useful for highly bound drugs that are difficult to reach equilibrium in equilibrium dialysis method.