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Pharmacology: Pharmacodynamics: Folic acid is a collective term for pteroylglutamic acids and their oligoglutamic acid conjugates. As a natural water-soluble substance, folic acid is involved in carbon transfer reactions of amino acid metabolism, in addition to purine and pyrimidine synthesis, and is essential for hematopoiesis and red blood cell production.
Pharmacokinetics: Absorption: Folic acid is rapidly absorbed from the gastrointestinal tract, mainly from the duodenum and jejunum.
Distribution: Folic acid is rapidly transported to tissues after intestinal absorption. Certain plasma proteins bind with folate derivatives but affinity is greater with non-methylated analogs. The role of plasma binding proteins in folate homeostasis is poorly understood.
Metabolism: Therapeutically administered folic acid enters the portal circulation mostly unchanged. Conversion to the active form 5-methyltetrahydrofolate occurs in the liver. The liver serves as the main storage site for folate. It is also actively concentrated in the cerebrospinal fluid.
Excretion: Folate undergoes enterohepatic circulation. Folate metabolites are excreted in the urine.
Folate in excess of body requirements is eliminated unchanged in the urine.
Folate is expressed in the breast milk.
Folic acid is removed by hemodialysis.
