Association between the pharmacokinetics of capecitabine and the plasma dihydrouracil to uracil ratio in rat: A surrogate biomarker for dihydropyrimidine dehydrogenase activity.

Capecitabine is a 5-fluorouracil (5-FU) derivative that is used widely in the treatment of colorectal cancer. The plasma ratio of dihydrouracil (UH ) 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.