ONO-2017 Study Japanese Patients With Primary Generalized Tonic Clonic Seizures.

Inclusion Criteria:

1. Gender and age: Japanese patients, regardless of gender, aged 18 years or older atthe time of informed consent.

2. Subject has a clinical diagnosis of Primary Generalized Tonic-Clonic (PGTC) seizuresin the setting of idiopathic generalized epilepsy.

3. Subject experiences at least 5 Primary Generalized Tonic-Clonic (PGTC) seizures in 12 weeks.

4. Subject is currently receiving 1 to a maximum of 3 concomitant AntiepilepticDrugs(AEDs) with fixed dosing regimens

Exclusion Criteria:

1. Subject has a history of status epilepticus that required hospitalization within 15months prior to enrollment.

2. Subject has seizure clusters where individual seizures cannot be countedorclassified.

3. History of non-epileptic or psychogenic seizures.

4. Subject has a concomitant diagnosis of Partial Onset Seizure(POS).

5. Subject has a history of any serious drug-induced hypersensitivity reaction (including but not limited to Stevens Johnson syndrome, toxic epidermal necrolysis,drug reaction with eosinophilia and systemic symptoms(DRESS), Drug-inducedhypersensitivity syndrome(DIHS)) or any drug-related rash requiring hospitalization.