Free fraction
The free fraction is a parameter in pharmacokinetics and receptor-ligand kinetics.
One speaks of two different free fractions:Plasma free fraction, previously referred to as Æ’1, is now referred to as Æ’P according to consensus nomenclature.Tissue free fraction, previously referred to as Æ’2
The plasma free fraction is the fraction of the ligand at equilibrium in blood plasma that is not bound to plasma proteins.