A drug used to treat or prevent seizures or convulsions that may be caused by epilepsy, brain surgery, or treatment for brain cancer. It is a type of anticonvulsant agent.

The sodium salt form of phenytoin, a hydantoin derivate and non-sedative antiepileptic agent with anticonvulsant activity. Phenytoin sodium promotes sodium efflux from neurons located in the motor cortex, thereby stabilizing the neuron and inhibiting synaptic transmission. This leads to a reduction in posttetanic potentiation at synapses, an inhibition of repetitive firing of action potentials and ultimately inhibits the spread of seizure activity.