A gas chromatographic assay for the determination of 5,6-dihydrofluorouracil and 5-fluorouracil in human plasma.

A gas chromatographic assay for the determination of 5-fluorouracil (5-FU) and 5,6-dihydrofluorouracil (FDHU) is described. The selectivity and sensitivity of the method allows the determination of both 5-FU and FDHU in 200 microliters of plasma. Diphenylsuccinimide and chlorouracil were used as external and internal standard, respectively. The assay including the extraction shows a good linearity in the range 0-5000 ng/ml plasma for 5-FU as well as for FDHU. 5-FU and FDHU plasma concentrations of a number of patients with breast cancer treated with 5-FU were determined in order to demonstrate the usefulness of the method.