Plasma protein binding of digitoxin and some other drugs in renal disease

Plasma protein binding of most acidic drugs is decreased in uraemia, whereas the binding of basic drugs is usually unchanged or decreased. Decreased protein binding in patients with renal disease mainly relates to drugs binding to albumin. Digitoxin binds to a specific site on the albumin molecule. Conflicting reports exist on digitoxin-protein binding in patients with renal disease. In ten patients with end-stage renal disease treated with haemodialysis we found only a slightly increased free fraction of digitoxin. A heparin-induced increase of the free fraction of digitoxin during haemodialysis has been reported. However, this increase was caused by the generation of non-esterified fatty acids in vitro. If this in vitro lipolysis was blocked, no increase of free digitoxin could be detected. Alterations of digitoxin-protein binding in uraemic patients during haemodialysis and during the intervals between haemodialysis treatments are small.