Adults

Typically 0.5-5 mg daily, depending on the condition. For folate deficiency anemia: 5 mg daily for 4 months. For prevention of neural tube defects: 0.4 mg to 5 mg daily (usually 5 mg if high risk).

Elderly

Same as adult dosage, no specific adjustment needed unless severe renal impairment.

Renal_impairment

No specific dose adjustment for mild to moderate impairment. Use with caution in severe impairment.

Onset

Within hours, clinical response (e.g., reticulocytosis) observed within 3-5 days.

Excretion

Mainly excreted in the urine as metabolites and unconjugated folic acid, particularly with higher doses.

Half life

Approximately several hours (e.g., 30 minutes to a few hours for reduced folates).

Absorption

Readily absorbed from the gastrointestinal tract, primarily from the proximal small intestine.

Metabolism

Metabolized in the liver to tetrahydrofolate and other reduced folates, which are metabolically active.

Methotrexate

Folic acid may interfere with the antifolate effects of methotrexate. Higher doses of folic acid may be required or administered at a different time.

Pyrimethamine

Reduced efficacy of pyrimethamine in malaria or toxoplasmosis treatment.

Sulfasalazine

May decrease folic acid absorption.

Phenytoin (and other anticonvulsants like carbamazepine, phenobarbital)

Folic acid can decrease the serum levels of phenytoin, potentially leading to increased seizure activity. Anticonvulsant dosages may need adjustment.