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Mephenytoin
Clinical data
AHFS/Drugs.com	Micromedex Detailed Consumer Information
MedlinePlus	a611020
Routes of; administration	Oral
ATC code	N03AB04 (WHO) ;
Pharmacokinetic data
Metabolism	CYP2C19
Elimination half-life	7 hours
Identifiers
	IUPAC name 5-Ethyl-3-methyl-5-phenyl-imidazolidine-2,4-dione;
CAS Number	50-12-4 ;
PubChem CID	4060;
IUPHAR/BPS	7223;
DrugBank	DB00532 ;
ChemSpider	3920 ;
UNII	R420KW629U;
KEGG	D00375 ;
ChEMBL	ChEMBL861 ;
CompTox Dashboard (EPA)	DTXSID9023257 ;
ECHA InfoCard	100.000.012
Chemical and physical data
Formula	C12H14N2O2
Molar mass	218.256 g·mol−1
3D 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) ; Key:GMHKMTDVRCWUDX-UHFFFAOYSA-N ;
	(verify)

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.

Mephenytoin is no longer available in the US or the UK. It is still studied largely because of its interesting hydroxylation polymorphism.

References

Shorvon SD, Fish DR, Perucca E, Dodson WE, eds. (2004). The Treatment of Epilepsy. Blackwell Publishing. ISBN 0-632-06046-8.
Resor SR (1991). The Medical Treatment of Epilepsy. Marcel Dekker. ISBN 0-8247-8549-5.
"Mephenytoin". The Comparative Toxicogenomics Database.