Quantitative determination of 1,3-bis(tetrahydro-2- furanyl)-5-fluoro-2,4-pyrimidinedione and its metabolites in plasma by high-pressure liquid chromatography and gas chromatography-mass fragmentography.

1,3-Bis(tetrahydro-2-furanyl)-5-fluoro-2,4-pyrimidinedione has been developed clinically as an antitumor agent. A high-pressure liquid chromatographic method was developed with which it could be measured in plasma with a sensitivity of 0.050 microgram/ml. Two of its metabolites, 1-(tetrahydro-2-furanyl)-5-fluoro-2,4-pyrimidinedione and 3-(tetrahydro-2-furanyl)-5-fluoro-2,4-pyrimidinedione, could be determined at the same time with a sensitivity of 0.025 microgram/ml. A gas chromatographic-mass fragmentographic method was developed for the specific determination of the third metabolite, 5-fluoro-2,4-pyrimidinedione, as its silylated derivative with a sensitivity of 0.001 microgram/ml. The precision and sensitivity of the assay appear to be satisfactory for determination of the plasma level of the drug.