Effects of 5-fluorouracil on the thiamin status of adult female rats.

The effect of 5-fluorouracil on the thiamin status of normal female adult rats has been investigated. Pre-treatment of the animals with the cytotoxic drug daily for 3 successive days resulted in a significant decrease in hepatic concentrations of thiamin concomitant with a decrease in thiamin-dependent transketolase enzyme activity and an increase in thiamin-pyrophosphate-(TPP-)stimulating effect in whole blood when compared with those of pair-fed control animals. The TPP effect of transketolase enzyme activity was also increased by 5-fluorouracil in vitro. Furthermore, the treatment with 5-fluorouracil resulted in decreased liver and spleen concentrations without affecting the urinary excretory levels of thiamin in animals supplemented with large doses of the vitamin. Giving a dose comparable to a human therapeutic dose caused a similar increase in the TPP effect. These results indicate that treatment with 5-fluorouracil may be associated with thiamin deficiency by increasing either the utilization or the breakdown of thiamin.