ABSTRACT
Protein binding is commonly defined as the reversible association of a drug to the proteins of blood, or more usually plasma. When a drug is administered intravenously or reaches the blood circulation after absorption, it interacts with the available proteins in two different ways: by adsorption on the surface of the proteins or, more rarely, by covalent bonding with active chemical groups of the proteins. When the binding is reversible, there is a dynamic distribution with a transfer between proteins and plasma water. At equilibrium a certain fraction of the total drug amount is bound to plasma proteins. Any factors modifying the nature of the binding interactions (pH change, ionic strength, protein tertiary structure, temperature) and the presence of other competing ligands can modify the extent of binding.
