[Comparative bioavailability of fluorouracil and its prodrug, ftorafur, following intra-arterial, intravenous and preoral administration].

The blood-plasma levels in 28 patients, suffering from colorectal cancer with liver metastases, which were treated by a cyclic chemotherapy with fluorouracil (1) after p.o. and intraarterial (i.a.) administration of 1 or its prodrug ftorafur (2), respectively, were compared with those obtained after i.v. administration and the pharmacokinetics were calculated. In the case of 1 as well as of 2 the i.a. administration has been found to be optimal for distribution into the tumor tissue of liver metastases due to lowered blood-plasma concentrations. The absolute bioavailability, was 78% for p.o. and 57% for the i.a. administration of 1 respectively, and 98% for p.o. and 61% for the i.a. administration of 1 (given as 2), Accordingly, p.o. administration of both substances leads to therapeutical sufficiently high plasma levels with a steady state of css = 2.9 micrograms/ml/tss = 14 min for 1 and css = 3.5 micrograms/ml/tss = 20 min for 2.