Pharmacokinetics of 5-Fluorouracil Following Hepatic Intra-arterial Infusion in a VX2 Hepatic Metastasis Model

BACKGROUND: Hepatic intra-arterial infusion chemotherapy of 5-fluorouracil (5-FU) or fluorodeoxyuridine (FUDR) has been a treatment option for liver metastasis from colorectal cancer. However, an optimal administration schedule of 5-FU is still controversial. This study was conducted to evaluate a suitable schedule from the viewpoint of 5-FU metabolites and related enzymes. METHODS: 5-FU was infused into the hepatic artery of rabbits having hepatic deposits of VX2 tumor cells in a daily dose of 1, 4, or 8 mg/kg using various schedules. 5-FU, Thymidylate synthase (TS), TS inhibition rate (TSIR), and the amount of fluoro-RNA (F-RNA) were measured. RESULTS: A high concentration of 5-FU was detected in the tumors of the group that was administered a dose of 8 mg/kg. TSIR in the tumor was about two-fold higher in the rabbits that were administered a total dose of 8 mg/kg than in those that were administered doses of 4 mg/kg or less. F-RNA, ranging from 27 to 36 ng/mg RNA, was detected in the tumor of the rabbits that were administered a total dose of 8 mg/kg. No difference was observed between the short period and the continuous administration schedules of rabbits that were administered a dose of 8 mg/kg of 5-FU. However, DNA synthesis inhibition in normal hepatic tissue was more dependent on the administration schedule than on the total dose of 5-FU because TSIR was significantly higher with shorter periods of drug administration. CONCLUSION: Intermittent bolus administration of large doses of 5-FU might cause more severe hepatic impairment than continuous administration. These results suggest that hepatic intra-arterial infusion of 5-FU should be administered continuously for liver metastasis, although further experiments including a longer administration period of 5-FU are required.