Abstract
Capecitabine is a 5-fluorouracil (5-FU) derivative that is used widely in the treatment of colorectal cancer. The plasma ratio of dihydrouracil (UH2 ) to uracil (Ura) is expected to gain relevance as an indirect-response biomarker to estimate the activity of dihydropyrimidine dehydrogenase (DPD). The latter is a rate-limiting enzyme in the catabolism of 5-FU in the capecitabine-based regimen. However, the relationship between the pharmacokinetics of capecitabine and the plasma UH2 /Ura ratio is still unknown. This study evaluated the time-course alterations of the plasma UH2 /Ura ratio in rats treated with 180mg/kg capecitabine. The molar ratio tended to increase within 1.5h (1.85±0.76 at 1.5h after administration of capecitabine) and gradually recovered to its initial level (1.00±0.46). The results of the current study suggest that the plasma UH2 /Ura ratio temporarily increases following administration of capecitabine, possibly related to the DPD activity levels. The plasma UH2 /Ura ratio might assist in monitoring the alteration of DPD activity levels in capecitabine treatments.
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