The important physiological and pharmacological functions of proteins require the participation of small drug molecules. Small drug molecules can promote or inhibit the realization of protein functions through interaction with proteins, especially the combination of drugs with plasma proteins will affect the biological activity of drugs. Drugs bind to plasma proteins to varying degrees in the plasma, and the degree of binding can affect the absorption, distribution, metabolism, and excretion of the drug in the body, and then affect the pharmacodynamic behavior of the drug. Therefore, the determination of drug plasma protein binding rate is important for drug development.
Common drug plasma protein binding assays include: equilibrium dialysis, ultrafiltration, partition equilibrium, stable isotope-GC-MS, gel filtration, and spectroscopic techniques. Among them, the equilibrium dialysis method is the most commonly used method to determine the free concentration of drugs based on the principle of drug-binding equilibrium, and it is also a classic method for studying the plasma protein binding rate of drugs.
The protein is placed in a compartment and separated by a semi-permeable membrane. Large molecules such as protein cannot pass through the semi-permeable membrane, while free ligands in the system can pass freely. When equilibrium is reached, the free ligand concentrations on both sides are equal. If the total amount of free ligands in the system is known, the amount of free ligands bound to the protein can be calculated by measuring the concentration of free ligands in the protein-free compartment.
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