Some clinical implications of the protein binding of digoxin.

1 The binding of [(3)H]-digoxin to human plasma proteins was studied using both ultrafiltration and frontal analysis, to establish a suitable method for the measurement of digoxin-protein interaction, and to assess the effect of variations in digoxin protein binding on its distribution. 2 Using ultrafiltration, [(3)H]-digoxin was found to bind to plasma proteins to the extent of 30-40% over a concentration range of 0.001-1 ng/ml. Frontal analysis was unsuccessful in the measurement of digoxin protein binding. 3 Dilution experiments using plasma and human serum albumin suggested that variations in digoxin protein binding would be unlikely to cause significant alterations in the levels of free drug in the body. 4 The possible clinical implications of these results are discussed.