Pharmacokinetics of oral doxifluridine in patients with colorectal cancer

Aims and background: Doxifluridine is a new fluoropyrimidine that has excellent absorption by the gastrointestinal tract when given orally, The aim of the study was to determine the disposition of doxifluridine and fluorouracil when the former is given orally for 5 days and to assess whether their pharmacokinetics are influenced by demographic or biologic parameters. Methods and study design: Twenty colorectal cancer patients received levo-leucovorin, 25 mg orally on days 1-5, followed 2 hrs later by doxifluridine, 1200 mg/m(2); the cycle was repeated every 10 days, Doxifluridine and fluorouracil levels were measured by reverse-phase high-performance liquid chromatography during the first cycle of therapy, The lowest dose given over the first 24 hrs was 1750 mg and the highest was 2500 mg, Results: The distribution of doxifluridine parameters remained the same between days 1 and 5, with an AUC that ranged between 72.2 and 74.5 mmol h/l and a C max that remained in a narrow band of 67.1 to 68.3 mmol/l, In contrast, the variability of fluorouracil parameters increased from day 1 to day 5, with an AUC of respectively 5.46 and 7.52 mmol hll and a C max that increased from 5.81 on day 1 to 7.34 mmol/l on day 5, A significant correlation between the AUC of doxifluridine and fluorouracil was found on day 1 and on day 5 (P<0.001). None of the demographic or biologic parameters considered was significantly related to pharmacokinetic parameters. Fluorouracil levels remained low in comparison with levels measured after classical fluorouracil therapy, although detectable for a longer time, Conclusions: A large interpatient pharmacokinetic variability was observed without any significant correlation with the clinical parameters studied.