Measurement of plasma uracil using gas chromatography-mass spectrometry in normal 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. Validation 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 pyrimidine catabolic enzyme, dihydropyrimidine dehydrogenase. Calibration standards were prepared in human plasma using the stable isotope, [N-15(2)]uracil, to avoid interference from endogenous uracil and 10 mu M 5-chlorouracil was added as the internal standard. Published by Elsevier Science B.V.