ChEBI: Phenytoin is a imidazolidine-2,4-dione that consists of hydantoin bearing two phenyl substituents at position 5. It has a role as an anticonvulsant, a teratogenic agent, a drug allergen and a sodium channel blocker. It derives from a hydantoin.NCI Thesaurus (NCIt): Phenytoin is a hydantoin derivative and a non-sedative antiepileptic agent with anticonvulsant activity. Phenytoin potentially acts by promoting sodium efflux from neurons located in the motor cortex reducing post-tetanic potentiation at synapses. The reduction of potentiation prevents cortical seizure foci spreading to adjacent areas, stabilizing the threshold against hyperexcitability. In addition, this agent appears to reduce sensitivity of muscle spindles to stretch causing muscle relaxation.