Sensitive liquid chromatographic assay for the simultaneous determination of 5-fluorouracil and its prodrug, tegafur, in beagle dog plasma

A high-performance liquid chromatographic (HPLC) method has been developed for the simultaneous determination of 5-fluorouracil (5-FU) and its prodrug, tegafur (TF), in dog plasma. 5-FU, the internal standard, 5-bromouracil, and TF were separated on a C18 Spherisorb ODS2 column using isocratic elution with retention times of 4.4, 8.0 and 21.2 min, respectively. Detection by UV absorption at 260 nm gave a limit of quantitation of 4 μg/l for 5-FU in plasma. Calibration curves for 5-FU and TF were linear over the ranges of 4–160 μg/l and 0.48–19.2 mg/l, respectively. Intra- and inter-day precision over these concentration ranges were <10.9 and <13.6% for 5-FU and TF, respectively, with good accuracy for both compounds. The method was successfully applied to define plasma concentration–time curves of TF and 5-FU in dogs administered a single oral dose containing TF (100 mg) and uracil (224 mg).