The Effect of Cyclosporin Concentration on the Efficiency of in Vitro Technetium-99m Radiolabeling of Red Blood Cells

Abstract

Previous work suggested that the immunosuppressive drug cyclosporin (CsA) was associated with significant decreases in red blood cell (RBC) radiolabeling efficiencies. To test this relationship, we studied five normal, adult male subjects who had received a single oral dose of CsA. Blood samples were drawn at 0, 1, 2, and 4 hours postdosage. In vitro labeling of RBCs by a commercial stannous-pyrophosphate preparation method was done on all samples and the labeling efficiencies calculated. Mean labeling efficiency for all subjects was 95.7% ± 1.7%. CsA concentration was determined on these samples by fluorescent polarization immunoassay (with a polyclonal antibody which detects the parent compound and some metabolites), using an Abbott TDx. The concentrations ranged from 0 ng/ml at predose to peak concentrations up to 1,897 ng/ml postdose. We found no significant effect (r = 0.17) of CsA concentration in whole blood up to 1,897 ng/ml upon labeling efficiency of RBCs. This is contrary to the original work of Allen et al. We postulate that the stannous-pyrophosphate used in our labeling procedure may be responsible for overcoming binding difficulties encountered with CsA in previous work.