Free fraction
Encyclopedia
The free fraction is a parameter in pharmacokinetics
and receptor-ligand kinetics
.
One speaks of two different free fractions:
The plasma free fraction is the fraction of the ligand
at equilibrium in blood plasma
that is not bound to plasma proteins.T
Pharmacokinetics
Pharmacokinetics, sometimes abbreviated as PK, is a branch of pharmacology dedicated to the determination of the fate of substances administered externally to a living organism...
and receptor-ligand kinetics
Receptor-ligand kinetics
In biochemistry, receptor-ligand kinetics is a branch of chemical kinetics in which the kinetic species are defined by different non-covalent bindings and/or conformations of the molecules involved, which are denoted as receptor and ligand....
.
One speaks of two different free fractions:
- Plasma free fraction, previously referred to as ƒ1, is now referred to as ƒP according to consensus nomenclatureNomenclatureNomenclature is a term that applies to either a list of names or terms, or to the system of principles, procedures and terms related to naming - which is the assigning of a word or phrase to a particular object or property...
. - Tissue free fraction (ƒND), previously referred to as ƒ2
The plasma free fraction is the fraction of the ligand
Ligand
In coordination chemistry, a ligand is an ion or molecule that binds to a central metal atom to form a coordination complex. The bonding between metal and ligand generally involves formal donation of one or more of the ligand's electron pairs. The nature of metal-ligand bonding can range from...
at equilibrium in blood plasma
Blood plasma
Blood plasma is the straw-colored liquid component of blood in which the blood cells in whole blood are normally suspended. It makes up about 55% of the total blood volume. It is the intravascular fluid part of extracellular fluid...
that is not bound to plasma proteins.T