mephenytoin mephenytoin mephenytoin (marketed as mesantoin by novartis) is a hydantoin, used as an anticonvulsant. it was introduced approximately 10 years after phenytoin, in the late 1940s. the significant metabolite of mephenytoin is nirvanol (5-ethyl-5-phenylhydantoin), which was the first hydantoin (briefly used as a hypnotic). however, nirvanol is quite toxic and mephenytoin was only considered after other less toxic anticonvulsants had failed. it can cause potentially fatal blood dyscrasia in 1% of patients. mephenytoinclinical dataahfs/drugs.commicromedex detailed consumer informationmedlineplusa611020routes ofadministrationoralatc coden03ab04 (who) pharmacokinetic datametabolismcyp2c19elimination half-life7 hoursidentifiers iupac name 5-ethyl-3-methyl-5-phenyl-imidazolidine-2,4-dione cas number50-12-4 ypubchem cid4060iuphar/bps7223drugbankdb00532 ychemspider3920 yuniir420kw629ukeggd00375 ychemblchembl861 ycomptox dashboard (epa)dtxsid9023257 echa infocard100.000.012 chemical and physical dataformulac12h14n2o2molar mass218.256 g·mol−13d model (jsmol)interactive image smiles o=c2n(c(=o)nc2(c1ccccc1)cc)c inchi inchi=1s/c12h14n2o2/c1-3-12(9-7-5-4-6-8-9)10(15)14(2)11(16)13-12/h4-8h,3h2,1-2h3,(h,13,16) ykey:gmhkmtdvrcwudx-uhfffaoysa-n y (verify) mephenytoin is no longer available in the us or the uk. it is still studied largely because of its interesting hydroxylation polymorphism.