Folic Acid Flashcards
What class of drugs does folic acid belong to?
vitamins (single agents)
Pterins and derivatives
What are examples of other drugs in the same class as folic acid?
ascorbic acid
pyridoxin
cholecalciferol
vitamin A tablets
What is folic acid indicated for?
folate-deficient megaloblastic anaemia
prevention of neural tube defects
prevention of MTX induced adverse effects
prophylaxis in chronic haematological states and folate deficiency dialysis
What is the mechanmism of action of folic acid?
Folic acid is biochemically inactive, and is converted into THF and methyl-THF by dihydrofolate reductase.
These are transported across cells by receptor-mediated endocytosis and used to maintain normal erythropoiesis, synthesise purine and thymidylate nucleic aids, interconvert amino acids and to generate and use formate.
Folic acid requires Vit. B12 as a cofactor to normalise high homocysteine levels.
What are the main PK and PD parameters of folic acid?
PK:
rapidly absorbed from wall of proximal small intestine via PO as 5-methyl-THF metabolite
5-methyl-THF extensively binds to plasma proteins in portal circulation
There is enterohepatic circulation
~4-5μg excreted in urine/day
What are the precautions associated with folic acid use?
pregnancy Category A, safe in breast feeding
exclude Vitamin B12 deficiency before using folic acid to treat megaloblastic anaemia
chronic alcoholism, infants < 12 months
What is the dose of folic acid given?
For folate-deficient megaloblastic anaemia: 5mg OD for 4 months (adult, or until term in pregnancy women)
Up to 15mg/day may be required in malabsorption states
prophylaxis of chronic haemolytic states:
5mg every 1-7 days depending on underlying disease. (adult)
prophylaxis of folate deficiency in dialysis:
5mg every 1-7 days (adult)
What are the contraindications associated with folic acid use?
never give folic acid alone for pernicious anaemia and other vitamin B12 deficiency states as this may precipitate subacute combined degeneration of the spinal cord.
do not give in undiagnosed megaloblastic anaemia
do not give in folate dependent tumour
What are the adverse reactions associated with folic acid use?
uncommon: GI upset
Rare: hypersenstivity including bronchospasm, erythema, fever, rash, itch
What are the drug interactions associated with folic acid use?
aminosalicylates: absorption of foic acid may be reduced by sulfasalazine
antiepileptics: folates may reduce plasma concentration of phenobarbital and phenytoin
cytotoxics: avoid folates when using cytotoxics (advised by manufacturer)
What are the alarm bells associated with folic acid use?
do not initiate until vitamin B12 deficiency has been excluded
What monitoring is involved with folic acid use?
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