Protein binding of digitoxin, valproate and phenytoin in sera from diabetics.

Chronic hyperglycaemia results in glycation of serum albumin and might affect the binding of drugs. The aim of the present study was to compare, using an equilibrium dialysis method, the protein binding of therapeutic concentrations digitoxin, valproate and phenytoin in sera from 70 insulin-dependent diabetics and 25 controls. Drug concentrations were measured by fluorescence immunopolarisation. Glycated albumin was measured by laser nephelometry after affinity chromatography. In sera from diabetics, protein binding of digitoxin (88.8 versus 89.9%) was unchanged; the protein binding of valproate (75.2 versus 80.7%) and phenytoin (67.9 versus 75.3%) was significantly decreased, but with no correlation with the concentration of glycated albumin. We conclude that the difference in protein binding between diabetic and control sera is due to glucose-independent modification of albumin in diabetics.