Biochemical modulation of intraperitoneal fluorouracil by allopurinol-the effect on an experimental adenocarcinoma in the liver

In a rat liver tumour system with a nitrosoguanidine-induced carcinoma and in an in vitro system with the same tumour, the effect of allopurinol on the toxicity and antitumour effect of 5-fluorouracil (5-FU) was explored. Two doses of 5-FU, 30 and 60 mg/kg b.w. intraperitoneally (i.p.), were tested with a large dose of allopurinol subcutaneously (s.c.( (300 mg) in rats. The drugs were given for three consecutive days. The lethal toxicity of 60 mg 5-FU i.p. could not be counteracted by allopurinol. Allopurinol and 30 mg 5-FU reduced the tumour growth rate more than 5-FU alone. The spleen was smaller, as a sign of increased toxicity, without allopurinol. The concentration of allopurinol and its metabolites in the general circulation was high. In vitro, there was no additive or specific effect of allopurinol. These results indicate some in vivo metabolic modulation of 5-FU efficacy by allopurinol if 5-FU is administered intraperitoneally and allopurinol systemically.