Oral uracil and Ftorafur plus leucovorin: pharmacokinetics and toxicity inpatients with metastatic cancer

Purpose: To assess the pharmacokinetics of Ftorafur (tegafur, FT), 5-fluoro uracil (5-FU), and uracil in 31 cancer patients who were enrolled in phase I studies of oral uracil and FT (UFT). The correlation between pharmacokine tic parameters and toxic effects of UFT was evaluated. Methods: Uracil and FT were orally administered in a 4:1 molar ratio at FT doses of 200-400 mg/ m(2) per day. Patients also received leucovorin at 150 mg/day. Daily doses were divided into three doses and administered at 8-h intervals for 28 cons ecutive days. Plasma FT concentrations were measured by highperformance liq uid chromatography, and plasma 5-FU and uracil concentrations were determin ed using gas chromatography-mass spectrometry. National Institutes of Healt h Common Toxicity Criteria were used for assessment of toxicity. Results: T he concentrations of FT, 5-FU, and uracil showed wide interpatient variatio ns. Maximum plasma concentrations (Cp-max) of all three compounds were achi eved in 0.3 to 4.0 h. At the various study doses, the terminal half-life (t (1/2 beta)) Of FT ranged from 3.9 to 5.9 h, the area under the concentratio n-versus-time curve (AUC(0-6h)) ranged from 16,220 to 52,446 (ng/ml)h, the total clearance (Cl-T) ranged from 100 to 175 ml/min, and the steady-state volume of distribution (Vd(ss)) ranged from 18.3 to 28.71. The 5-FU generat ed from FT had an apparent distribution half-life (t(1/2 alpha)) and an app arent elimination half-life (t(1/2 beta)) of 0.3-1.3 h and 4.9-7.0 h, respe ctively. The AUC(0-6h) of 5-FU ranged from 120 to 325 (ng/ml)h, Uracil had a t1/2a Of 0.2-0.5 h and the level quickly returned to the endogenous level . The AUC(0-6h) for uracil ranged from 605 to 3764 (ng/ml)h, the Cl-T range d from 3225 to 7748 ml/ min, and the Vd(ss) ranged from 341 to 1354 l. The Cp-max and AUC(0-6h) Of both FT and uracil were significantly correlated wi th FT doses (P-values of 0.0244 and 0.0112) and with uracil doses (P-values of 0.0346 and 0.0083), respectively. In addition to interpatient variation s, intrapatient variations were also observed in six patients who had pharm acology studies done on days 1 and 26 +/- 2 at the same study dose. We foun d that the repeated treatment with UFT caused cumulative increases in the v alues of Cp-max, C-trough, and AUC(0-6h) Of FT and 5-FU. The major toxic ef fects observed were diarrhea and nausea and vomiting. The occurrence of the se toxic effects correlated significantly with the Cp-max and AUC(0-6h) Of 5-FU. Conclusions: The pharmacology studies showed that FT and uracil were readily absorbed orally and that FT was rapidly converted to 5-FU. The prel iminary findings suggest that determination of plasma levels of 5-FU after oral administration of UFT may help predict subsequent toxic effects.