text: Folinic acid is also used in combination with the chemotherapy agent 5-fluorouracil in treating colon cancer. In this case, folinic acid is not used for "rescue" purposes; rather, it enhances the effect of 5-fluorouracil by inhibiting thymidylate synthase.
  Folinic acid is also sometimes used to prevent toxic effects of high doses of antimicrobial dihydrofolate reductase inhibitors such as trimethoprim and pyrimethamine, although its value for this indication has not been clearly established.  It may be prescribed in the treatment of toxoplasmosis retinitis, in combination with the folic acid antagonists pyrimethamine and sulfadiazine.
  Folinic acid is also used in the treatment of cerebral folate deficiency, a syndrome in which the use of folic acid cannot normalize cerebrospinal fluid levels of 5-MTHF.
  In pyridoxine-dependent epilepsy, folinic acid may be used as additional therapy if pyridoxine or pyridoxal phosphate fails to fully control the seizures.
  Side effects
  Folinic acid should not be administered intrathecally. This may produce severe adverse effects or even death.
  In cancer patients, rare hypersensitivity reactions to folinic acid have been described.
  Drug interactions
  Fluorouracil: Folinic acid may increase the toxicity associated with fluorouracil if the two are administered together. Some adverse effects that have occurred, particularly in elderly patients, include severe enterocolitis, diarrhea, and dehydration.