Dilantin is an anticonvulsant drug and sometimes it is known as an antiepileptic medication. It is prescribed to those who have seizures that are brought by abnormal electrical brain activity. This medication works by reversing the electricity charges move in the cell. It also helps in the reduction of these seizures. Dilantin (extended phenytoin sodium capsule) is a hydantoin derivative anticonvulsant drug. Dilantin is used to treat generalised tonic-clonic (grand mal) seizures, complex partial seizures (temporal lobe or psychomotor) and in preventing seizures after neurosurgery or head injury.