High-performance liquid chromatographic column-switching method for two cyclosporine metabolites in blood

Cyclosporine (CSA) is biotransformed to many metabolites which may contribute to its immunosuppressive and nephrotoxic activity. We report a rapid and sensitive, automated column-switching high-performance liquid chromatographic (HPLC) method for measuring CSA-M17 in whole blood; the method also separates CSA-M1. CSA metabolite standards were isolated by a preparative-scale HPLC method. Samples were prepared by protein precipitation with acetonitrile followed by dilution with water. CSA-M17 was initially separated on a C8 column; final separation was on a C18 column. The inter-day relative standard deviation at 50 ng/ml was 8% (n = 3). Limit of detection was 20 ng/ml.