Does renal failure induce a decrease in cyclosporine blood concentrations?

Blood Cys concentrations were monitored twice weekly by RIA in nine patients undergoing renal transplantation. The Cys dose was adapted to obtain blood values between 100-400ng/ml. A negative correlation was found between plasma creatinine and blood Cys, even in those patients in whom the oral dosage was not changed (r = 0.65, n = 23, p less than 0.001). In vitro studies showed no effect of uraemic blood on Cys measurement. It seems probable that uraemia induces changes in distribution volume and/or gastrointestinal absorption of the drug. Careful monitoring of Cys during uraemia is therefore warranted.