Digitoxin protein binding in patients on hemodialysis

Abstract

A reduction of digitoxin binding to plasma proteins during hemodialysis has been reported. Our aim was to determine whether this reduction is an in vivo effect or occurs only after blood collection as a result of heparin-induced lipolysis which increases levels of non-esterified fatty acids in vitro. Digitoxin protein binding was studied in 10 patients undergoing hemodialysis, receiving digitoxin maintenance therapy. Digitoxin free fraction was increased at the end of hemodialysis, from 2.5 ± 0.7% to 4.4 ± 1.1%, but after inhibition of in vitro lipolysis with paraoxon (2 mmol/1), a potent lipase inhibitor, there was no increase in the free fraction: 2.3 ± 0.4% before heparin and 2.4 ± 0.5% at the end of hemodialysis. Digitoxin salivary levels were also unchanged: 0.41 ± 0.08 ng/ml before heparin and 0.41 ± 0.08 ng/ml at the end of hemodialysis (n = 8). These data indicate that the binding of digitoxin in vivo is not altered during hemodialysis. The reduced binding reported elsewhere was a result of heparin-induced in vitro lipolysis.