Correlation between the Urinary Dihydrouracil-uracil Ratio and the 5-FU Plasma Concentration in Patients Treated with Oral 5-FU Analogs

Background: The determination of dihydropyrimidine dehydrogenase (DPD) deficiency is important in avoiding severe 5-fluorouracil (FU) toxicity. The dihydrouracil (UH2)-uracil (Ura) ratio (UH2/Ura) in plasma might be an important indicator of the risk of 5-FU catabolic deficiency. In order to clarify this possibility, the pyrimidine metabolites and the UH2/Ura were measured in urine and the plasma level of 5-FU was evaluated in patients with gastric and colorectal cancer. Patients and Methods: Patients with primary gastric (n=14) and colorectal (n=8) cancer who had undergone surgery were recruited in this study. These patients were divided into the S-1 treatment group, which drug is a novel oral formulation of tegafur, oxonic acid and 5-chloro-2, 4-dihydroxypyridine (CDHP) (n=14) and a group receiving other drugs which include UFT (Uracil/Tegafur) or oral doxifluridine (n =8). The urinary levels of UH2 and Ura were measured by high-performance liquid chromatography (HPLC) using column swiching. The plasma level of 5-FU was assessed by gas chromatography-mass spectrometry (GC-MS). Results: The UH2/Ura or UH2/Ura (treated/no treated) in the S-1 group significantly decreased in comparison to that in the other-drug group and the plasma 5-FU concentration in the S-1 group significantly increased compared to that in the group treated with other drugs. The plasma 5-FU concentration levels significantly indicated a positive correlation with urinary Ura. Moreover, UH2/Ura treated with 5-FU analogs or UH2/Ura (treated/no treated) significantly showed a negative correlation with the plasma 5-FU concentration levels. Conclusion: Our findings indicate that either urinary Ura, the UH2/Ura or UH2/Ura (treated/no treated) can predict the plasma 5-FU concentration levels or DPD deficiencies.