Drugs and plasma proteins
The main influence of plasma proteins on drugs is in their distribution. The most important plasma proteins in this context are albumin, acid-glycoprotein and beta-globulin.
Once a drug has been absorbed into the circulation it may become attached (we say bound) to plasma proteins. However this binding is rapidly reversible and non-specific – that is many drugs may bind to the same protein.
It is important to recognise that plasma proteins do not represent target tissues and drug binding produces no physiological effect. Drug-plasma protein binding forms a "reservoir" of drug, but only the free (unbound) drug is available to the tissues to exert a therapeutic effect.