L-Folinic acid is a reduced folic acid and isomer of DL-folinic acid . DL-Folinic acid is a racemic mixture of D-folinic acid and L-folinic acid that has been used to prevent toxicity following therapy with high-dose methotrexate , to enhance the antitumor activity of 5-fluorouracil , and as a folate supplement. Clinical studies demonstrate that formulations containing L-folinic acid have similar efficacy and tolerability as those contianing DL-folinic acid and have been used interchangeably for modification of antitumor activity of 5-fluorouracil, while D-folinic acid is inactive.
