A sensitive method for determination of 5-fluorouracil and 5-fluoro-2'-deoxyuridine in human plasma by high-pressure liquid chromatography

A high-pressure liquid chromatographic method which is capable of measuring 5-fluorouracil and 5-fluorodeoxyuridine at concentrations of 50 nM in human plasma is presented. The method employs tritium-labeled 5-fluorouracil and 5-fluorodeoxyuridine as internal standards. The fluoropyrimidines are removed from plasma by anion-exchange chromatography and are extracted into ethyl acetate. The ethyl acetate is evaporated to dryness and 5-fluorouracil and 5-fluorodeoxyuridine are chromatographed on a semipreparative μBondapak C₁₈ column. The method is specific and sufficiently sensitive to measure the levels of 5-fluorouracil in plasma below 1 μM as found after intrahepatic or intraperitoneal drug administration.