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Calcium Folinate should only be used with methotrexate or 5-FU under the direct supervision of a clinician experienced in the use of cancer chemotherapeutic agents.
In the treatment of inadvertent overdosage of a folic acid antagonist, folinate should be administered as soon as possible; if a period exceeding 4 hours intervenes, the treatment may not be effective.
In general, Calcium Folinate should not be given simultaneously with folic acid antagonists, e.g. methotrexate, to abort clinical toxicity as the therapeutic effect of the antagonist may be nullified. However, Calcium Folinate given concurrently with folate antagonists, such as pyrimethamine and trimethoprim does not inhibit their antibacterial activity.
Parenteral administration of folinate is preferable to oral dosing following chemotherapy with folic acid antagonists if there is a possibility that the patient may vomit and not absorb the folinate.
Measures to ensure the prompt excretion of methotrexate are important as part of Calcium Folinate Rescue Therapy.
These measures include: 1) Alkalinisation of urine so that the urinary pH is greater than 7.0 before methotrexate infusion (to increase solubility of methotrexate and its metabolites).
2) Maintenance of urine output of 1800-2000 cc/m2/24 hr by increased oral or intravenous fluids on days 2, 3 and 4 following methotrexate therapy.
3) Plasma methotrexate concentration, BUN and creatinine should be measured on days 2, 3 and 4. These measures must be continued until the plasma methotrexate level is less than 10-7 molar (0.1 μM).
