DrugindexOnline^{2nd edition}

Pronouncation: (FOE-lik AH-sid)
Class: Vitamin

Trade Names:
Folic Acid
- Tablets 0.4 mg
- Tablets 0.8 mg
- Tablets 1 mg

Trade Names:
Folvite
- Tablets 1 mg
- Injection 5 mg/mL

Apo-Folic (Canada)

Mechanism of Action

Pharmacology

Required for nucleoprotein synthesis and maintenance of normal erythropoiesis; precursor of tetrahydrofolic acid, which is necessary for transformylation reactions in the biosynthesis of purines and thymidylates of nucleic acids.

Pharmacokinetics

Absorption

T _max occurs within 1 h. Absorption occurs primarily in the proximal portion of the small intestine.

Metabolism

Folic acid is metabolized in the liver to 7,8-dihydrofolic acid and eventually to 5,6,7,8-tetrahydrofolic acid.

Elimination

Up to 90% is excreted in the urine and small amounts in the feces.

Serum concentrations

Normal serum levels of folate are about 5 to 15 ng/mL; CSF levels are about 16 to 21 ng/mL; levels below 5 ng/mL indicate folate deficiency and levels below 2 ng/mL usually result in megaloblastic anemia.

Indications and Usage

Megaloblastic anemia caused by folic acid deficiency, as may be seen in tropical or nontropical sprue, and in anemias of nutritional origin, pregnancy, infancy, or childhood.

Contraindications

Treatment of pernicious anemia and other megaloblastic anemias where vitamin B ₁₂ is deficient (not effective).

Dosage and Administration

Therapeutic Dose
Adults and children

PO/IV/IM/Subcutaneous Up to 1 mg/day. Resistant cases may require larger doses; except during pregnancy and lactation, do not give therapeutic doses greater than 0.4 mg daily until pernicious anemia has been ruled out. May need to be increased in alcoholism, hemolytic anemia, anticonvulsant therapy, or chronic infection.

Maintenance Dose
Adults and children 4 yr of age and older

PO/IV/IM/Subcutaneous 0.4 mg/day.

Pregnant and lactating women

0.8 mg/day

Children younger than 4 yr of age

PO/IV/IM/Subcutaneous Up to 0.3 mg/day.

Infants

PO/IV/IM/Subcutaneous 0.1 mg/day.

General Advice

• Injection
• Generally used when anemia is exceptionally severe, or if GI absorption may be, or is known to be, impaired.
• For subcutaneous, IM, or IV administration only. Not for intradermal or intra-arterial administration.
• Do not administer if particulate matter, cloudiness, or discoloration noted.

Storage/Stability

Store injection and OTC tablets at controlled room temperature (59° and 86°F). Store 1 mg tablets at controlled room temperature (68° to 77°F). Protect tablets from light and moisture. Protect injection from light.

Drug Interactions

Phenytoin

Reduced effect caused by folic acid.

Sulfasalazine

May reduce absorption of folic acid.

Laboratory Test Interactions

False low serum and red cell folate levels may occur if coadministration with antibiotics (eg, tetracycline) have occurred.

Adverse Reactions

Hypersensitivity

Anaphylaxis; allergic responses have included erythema, skin rash, itching, generalized malaise, and respiratory difficulty caused by bronchospasm.

Precautions

Pregnancy

Category A . Is recommended for women who are contemplating pregnancy or who are pregnant to avoid birth defects caused by folic acid deficiency.

Lactation

Excreted into breast milk.

Benzyl alcohol

Injection is preserved with benzyl alcohol, which has been associated with a fatal gasping syndrome in premature infants.

Undiagnosed anemia

Folic acid doses higher than 0.1 mg/day may obscure diagnosis of pernicious anemia by alleviating the hematologic manifestations of the disease. Doses higher than 0.1 mg/day should not be used unless anemia caused by vitamin B ₁₂ deficiency has been ruled out or is being adequately treated with cobalamin.

Overdosage

Symptoms

Oral doses of 15 mg daily have produced anorexia, nausea, abdominal distention, flatulence, biter/bad taste, altered sleep patterns, difficulty in concentrating, irritability, over activity, excitement, mental depression, confusion, impaired judgment.

Patient Information

• Injection
• Advise patient or caregiver that medication will be prepared and administered by a health care professional in a health care setting when oral therapy is not feasible, but that therapy will be switched to oral when it is appropriate.

• OTC Tablets
• Caution patient not to use OTC folic acid unless advised by health care provider.
• Instruct patient using OTC tablets to carefully read package instructions regarding warnings and dosing instructions.

• Prescription Tablets
• Advise patient to take prescribed dose without regard to meals, but to take with food if stomach upset occurs.
• Caution patient not to change or stop taking the dose unless advised by health care provider.