Plasma binding

The pharmacokinetic and pharmacodynamic properties of drugs are largely a function of the binding of drugs to plasma proteins. High drug-protein binding can both reduce the amount of free drug available for target sites and prolong the duration of drug activity. Only the unbound drugs are available for transport across cell membranes for interaction with a pharmacological target such as receptors, enzymes or ion channels and distribution to other organs and tissues. Plasma protein bound drugs show low level of distribution since they are assembled mainly in the vascular space. In vitro plasma protein binding testing offers methods to determine percentage drug bound to plasma proteins.