Folinic acid (calcium folinate)

How it works

As an already-reduced folate it bypasses the dihydrofolate reductase step blocked by methotrexate, restoring folate-dependent synthesis in normal cells and so limiting antifolate toxicity.

Prescribing in practice

• Folinic acid rescue must be given at the correct time and dose relative to methotrexate, because delayed or inadequate rescue can result in life-threatening methotrexate toxicity.
• It is used to treat overdose or accidental overexposure to folate-antagonist drugs and certain methotrexate-induced toxicities.
• It does not reverse the antifolate effect of trimethoprim-sulfamethoxazole on a treated infection in the way that simple folate supplementation would, and product-specific guidance should be followed.

Monitoring

In methotrexate rescue, monitor methotrexate plasma levels and renal function to determine the duration and intensity of folinic acid cover.

Counselling the patient

• This is a rescue medicine that protects healthy cells from chemotherapy toxicity.
• It must be taken exactly on schedule after methotrexate.
• Report mouth ulcers, vomiting or feeling very unwell after methotrexate treatment.

Evidence & guidelines

Folinic acid (calcium folinate) rescue is the established standard for limiting toxicity after high-dose methotrexate and in folate-antagonist overdose.