Final answer:
Phenytoin is used therapeutically to diminish seizure activity and terminate ventricular arrhythmias.
Step-by-step explanation:
The therapeutic use of Phenytoin is to diminish seizure activity and terminate ventricular arrhythmias. Phenytoin is an anticonvulsant medication commonly used to treat various types of seizures, including generalized tonic-clonic seizures and partial seizures. It works by stabilizing the electrical activity in the brain and preventing the abnormal firing of neurons that can lead to seizures.