Aspects of the reversal of methotrexate toxicity in rodents

An ip injection of a Lactobacillus casei dihydrofolate reductase preparation into rats and mice given a single lethal dose of methotrexate (MTX) caused a marked lowering of free MTX in the blood. Alternatives to citrovorum factor as agents for reversing MTX toxicity were explored in mice. dl, L-5-Methyltetrahydrofolate, dl,L-5,10-methylenetetrahydrofolate, l,L-5,10-methylenetetrahydrofolate, and dihydrofolate were also effective MTX antagonists; d,L-5,10-methylenetetrahydrofolate was inert.