Fosphenytoin sodium (CAS NO.: ), with its systematic name of 2,4-Imidazolidinedione, 5,5-diphenyl-3-((phosphonooxy)methyl)-, disodium salt, could be produced through many synthetic methods.

Following is one of the synthesis routes:
5,5-Diphenylhydantoin (phenytoin) (I) reacts with formaldehyde in the presence of K₂CO₃ in water to produce 3-(hydroxymethyl)-5,5-diphenylhydantoin (II), which is treated with PCl3 in dichloromethane to afford 3-(chloromethyl)-5,5-diphenylhydantoin (III). The condensation of (III) with silver dibenzyl phosphate (IV) in refluxing benzene yields dibenzyl 5,5-diphenylhydantoin-3-ylmethyl phosphate (V), which is converted to the corresponding free phosphoric acid (VI) by reduction with H₂ over Pd/C in ethyl acetate. Finally, this compound is treated with NaOH in methanol.