Folic Acid
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Pharmacy
Starting dose
0.4 mg PO daily (general prevention); 0.8-1 mg/d in pregnancy; 4 mg/d for women with prior NTD-affected pregnancy; 1 mg/d during methotrexate therapy
Preparations
0.4, 0.8, 1 mg OTC; 1 mg Rx; 5 mg/mL injection
US FDA Max
1 mg/d typical Rx; higher in specific indications
Pharmacology
Routes
Oral, IM, IV, SC
Onset
Hematologic response within days
Duration
N/A (replacement)
Half-life
~0.5 hours plasma; tissue retention longer
Bioavailability
High (oral)
Pregnancy
Routinely supplemented in pregnancy and preconception to prevent neural tube defects.[citation needed]
Legal status
OTC (low-dose) and Rx-only (1 mg, injectable) in US
Purported mechanism
Folic acid is the synthetic form of folate; following absorption it is reduced by dihydrofolate reductase to tetrahydrofolate (THF), the carrier of one-carbon units required for thymidylate, purine, and amino acid synthesis.0 The dramatic effect on neural tube defects (Medical Research Council Vitamin Study, 1991) led to US mandatory cereal-grain fortification (1998) and population-level NTD reduction. In folate-deficient megaloblastic anemia presenting with neurologic symptoms, B12 deficiency must be excluded first because folate alone will correct anemia while masking and potentially accelerating B12-deficient subacute combined degeneration[1].
References
[edit | edit source]- ↑ FDA Prescribing Information, folic acid tablets, current revision. https://www.accessdata.fda.gov/drugsatfda_docs/label/2003/06006slr027_folvite_lbl.pdf