MEASUREMENT OF CYCLOSPORINE-A BY A SPECIFIC RADIOIMMUNOASSAY WITH A MONOCLONAL-ANTIBODY AND I-125 TRACER

We developed a sensitive radioimmunoassay (CYCLO-Trac(R) SP) that specifically measures cyclosporine A in serum, plasma and whole blood of transplant patients. The specific monoclonal antibody was from Sandoz and the tracer was an I-125 derivative of cyclosporine C. The assay is performed at room temperature for 1 h followed by a 20 min centrifugation. The sensitivities of the assays are 2.6 ng/mL and 8.7 ng/mL for the serum/plasma assay and the whole blood assay, respectively. Within-run and between-run CVs for both types of assays using cyclosporine concentrations of 80 and 58 ng/mL (serum) and 186 and 199 ng/mL (whole blood) were less than 5% and 9%, respectively. Averaged recovery of serum/plasma and whole blood assays at various levels ranged from 93% to 115%. Interferences by bilirubin, triglyceride, cholesterol, hemoglobin, OKT-3, azathioprine, methylprednisolone and 20 other drugs were insignificant. Multicenter proficiency studies showed an excellent correlation between the CYCLO-Trac(R) SP and the specific H-3-Sandimmune(R) assay from Sandoz: whole blood assay (r = 0.998) and serum assay (r = 0.997).