As protein binding , and plasma protein binding (PPB) or plasma protein binding (PEB) mentioned, which is reversible binding of substances of protein components of the blood ( plasma proteins , erythrocyte proteins ) or said body tissue , respectively. Various forms of chemical bonds can be involved in this protein bond, namely ionic bonds , hydrogen bonds , dipole-dipole interactions and hydrophobic interactions. As a result of protein binding, the bound substances, including drugs and various endogenous substances, do not have their normal effect or only do so to a limited extent, since they cannot react with the environment as they normally would. The part of a substance bound by proteins is therefore pharmacologically inactive. Small molecules have a greatly extended half-life when they bind , so they are excreted via the kidneys only very slowly .
The substances that are largely bound to proteins in the plasma include, for example, the drugs sulfonamides , sulfonylureas , acetylsalicylic acid , phenylbutazone , coumarins and the body's own substances bilirubin and calcium .
The total amount of a substance that can be bound is limited by the capacity of the proteins. By displacing one another from the plasma protein binding, substances can mutually increase their effectively effective (since not bound) concentration in the blood ( synergism ). For this reason, amplify, for example, sulfonamides to newborn jaundice by displacement of bilirubin from albumin and are therefore contraindicated in neonates. When different drugs are administered, drug interactions based on this principle can lead to the occurrence of undesirable drug effects ( side effects ).