Determination of cyclosporine in plasma: specific radioimmunoassay with a monoclonal antibody and liquid chromatography compared.

A radioimmunoassay of cyclosporine (Sandimmune) involving use of a mouse monoclonal antibody was tested to monitor specifically the parent drug in plasma. The cyclosporine concentrations obtained by RIA were compared with those obtained by the HPLC method. For the RIA method, the within- and between-assay CVs are less than 6%, the limit of detection is about 10 micrograms/L for a 50-microL sample of plasma. For the HPLC method, the within- and between-assay CVs are less than 20%, the limit of detection is about 15 micrograms/L for a 1-mL sample of plasma. The concentrations by RIA correlated well with those by HPLC in samples from patients receiving bone-marrow (n = 39), heart (n = 52), or liver (n = 51) transplants. In all indications, the ratio of values by RIA to those by HPLC for these samples remained stable and close to 1 during the drug-monitoring period, i.e., for up to 202 days. Therefore, the specific RIA can be used instead of HPLC to measure the parent drug in plasma.