The binding of drugs to plasma proteins and the interpretation of measurements of plasma concentrations of drugs in patients with poor renal function.

The intensity of a drug's action is related to its concentration in plasma water. Since the analytical methods for determining concentrations of drugs in plasma measure this as well as the drug bound to plasma proteins, evaluation of the binding of drugs to plasma proteins is needed for proper interpretation of drug level measurements. Anionic drugs have decreased binding in plasma from patients with renal failure. With some, such as phenytoin, a reduction is required in the levels usually considered "therapeutic" for uremic patients. Basic drugs may have normal or decreased binding. Propranolol, quinidine and tricyclic antidepressants are drugs in this class that have normal binding and that do not require changes in the plasma levels usually considered "therapeutic" for these patients.