Folic acid supplementation in folate-deficient patients with epilepsy changes the pharmacokinetics of phenytoin
, usually leading to lower serum phenytoin
concentrations and possible seizure breakthrough..."
It however says that initiation of Folic acid and phenytoin together is beneficial.
Since you can't go back and start all over again, you can take a small dose. It has been observed that as los as 1mg dose can perturb phenytoin’s levels
, You may take doses lower than 1mg/day.