Determination of cyclosporine A in whole blood: comparison of a chromatographic method with three different immunological methods.

Cyclosporine A is potent immunosuppressive agent characterized by a narrow therapeutic range, inter- and intra-individual variability and a lack of correlation between drug dosage and blood levels. In view of these facts, blood levels of CyA should be routinely monitored to assess organ rejection and toxicity. We evaluated CyA as well as its metabolites (AM9, AM19, AMl, and AM4N) in whole blood samples from 117 patients using commercially available immunological assays (AxSYM, EMIT, Dimension) and HPLC. Cross-reactivity of the immunological assays was evaluated using different concentrations of the CyA metabolites (in vitro cross-reactivity) and by statistical analysis of patient data (in vivo cross-reactivity). Cross-reactivity was seen in all immunological assays, with differences in in vitro and in vivo cross-reactivity. The statistical analysis showed a classical correlation between HPLC and AxSYM of r(2)=0.89, HPLC versus EMIT of r(2)=0.93, and HPLC versus Dimension of r(2)=0.93. The percentage metabolite cross-reactivity (%) by immunological assays for four metabolites at two concentrations each (250 and 1000 ng ml(-1)) was lowest with the Dimension assay. Of the immunological methods examined, the new Dimension for CyA determination can be relied on to produce results comparable to HPLC; other advantages are its simplicity, practicability and ease of handling.