Measurement of plasma uracil using gas chromatography-mass spectrometry innormal individuals and in patients receiving inhibitors of dihydropyrimidine dehydrogenase

A sensitive gas chromatographic-mass spectrometric method is described for reliably measuring endogenous uracil in 100 mu l of human plasma. Validatio n of this assay over a wide concentration range, 0.025 mu M to 250 mu M (0. 0028 mu g/ml to 28 mu g/ml), allowed for the determination of plasma uracil in patients treated with agents such as eniluracil, an inhibitor of the py rimidine catabolic enzyme, dihydropyrimidine dehydrogenase. Calibration sta ndards were prepared in human plasma using the stable isotope, [N-15(2)]ura cil, to avoid interference from endogenous uracil and 10 mu M 5-chlorouraci l was added as the internal standard. Published by Elsevier Science B.V.