Phenytoin Causing Folate Deficiency.

Phenytoin ('Dilantin') inhibits folate absorption from folate polyglutamates, a major component of food folate, and inhibits the activity of folate conjugase from human jejunal mucosa.

Folate conjugase is thought to split dietary folate polyglutamates into the simpler folate monoglutamate form before absorption and it is therefore likely that phenytoin reduces absorption of folate polyglutamates by inhibiting this enzyme.