Protein binding of piretanide in normal and uraemic serum

The protein binding of piretanide was assessed by continuous ultrafiltration of sera from six normal subjects and seven uraemic subjects (samples taken immediately pre-dialysis). Throughout the range of piretanide concentrations studied (0.5-4.5mM), the mean protein binding for uraemic serum was less than that for normal serum. This difference was significant (p less than 0.05) at piretanide concentrations of 1.5 mM and above, but not at 1mM where mean protein binding for uraemic serum was 88.1% compared to 94.2% for normal serum. Analysis of piretanide protein binding characteristics using the Rosenthal plot showed no significant differences between uraemic and normal serum with respect to primary or secondary binding sites. Parallel assessment by the Scatchard method suggests, as expected, that albumin is the principle protein moiety responsible for binding piretanide.