High-performance liquid chromatographic determination of the enantiomers of cyclophosphamide in serum

A high-performance liquid chromatographic (HPLC) achiral-chiral coupled assay to measure the serum concentration of the enantiomers of cyclophosphamide is described. The R- and S-enantiomers of cyclophosphamide were quantified using a 5-cm-long C-1 Spherisorb 5-mu m column, with switching of the eluent containing racemic cyclophosphamide onto a 10-cm-long alpha(1) acid glycoprotein column. The limit of determination was 1.25 mg l(-1) for each enantiomer and the ratio of the enantiomers over the range 2.5 to 100 mg l(-1) was 1. Serum enantiomer concentrations in blood samples taken from patients receiving 0.30 to 0.75 g m(-2) of intravenous racemic cyclophosphamide could be measured at least three half-lives post dose. In six patients no significant difference in the clearance of R- and S-cyclophosphamide was found.