DESCRIPTION
MECHANISM OF ACTION
Leucovorin is folic acid in its active (reduced) form, so it allows nucleic acid synthesis to proceed even in the presence of
methotrexate. Leucovorin can also compete with methotrexate for the same transport processes into the cell.
ABSORPTION
Following oral administration, leucovorin is rapidly absorbed and expands the serum pool of reduced folates. At a dose of 25 mg, almost 100%
of the l-isomer but only 20% of the d-isomer is absorbed. Oral absorption of leucovorin is saturable at doses above 25 mg.
INDICATIONS
Leucovorin calcium is indicated in the treatment of megaloblastic anemias due to folic acid deficiency when oral therapy is not feasible. Leucovorin
is also indicated for use in combination with 5-fluorouracil to prolong survival in the palliative treatment of patients with advanced colorectal cancer.
DRUG INTERACTION
Excessive amounts of leucovorin may nullify the chemotherapeutic effect of folic acid antagonists. Leucovorin is improper therapy for
pernicious anemia and other megaloblastic anemias secondary to the lack of vitamin B12.
SPECIAL CONSIDERATIONS
1Why does leucovorin need to be given on time?
Doses of leucovorin rescue will be ordered at evenly spaced intervals, and it is critical to administer those on time.
Severe immunosuppression and toxicity can occur if doses are missed or not given on time.
TOXICITY 1
Doses higher than those recommended for oral use must be given intravenously. Leucovorin may enhance the toxicity of fluorouracil.
Deaths from severe enterocolitis, diarrhea, and dehydration have been reported in elderly patients receiving weekly leucovorin and fluorouracil.
SPECIFICATION
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