Which vitamin supplementation is known to decrease phenytoin blood levels?

Folic acid is known to decrease phenytoin blood levels due to its role in metabolic processes. Phenytoin, an antiepileptic medication, is highly protein-bound and has a narrow therapeutic window. The concurrent use of folic acid can enhance the metabolism of phenytoin, leading to reduced serum concentrations of the drug. This occurs because folic acid may increase the activity of certain enzymes in the liver that metabolize phenytoin, thus leading to its decreased blood levels.

Adequate levels of folate are particularly important during pregnancy to prevent neural tube defects; however, when patients on phenytoin initiate folic acid supplementation, close monitoring of phenytoin levels is essential to ensure that therapeutic levels are maintained to avoid seizure recurrence. This interaction highlights the intricate balance between maternal supplementation and medication management in pregnant patients with epilepsy.