A Placebo-Controlled, Double-Blind Comparative Study of E2080 in Lennox-Gastaut Syndrome Patients (Study E2080-J081-304)

Inclusion criteria 1. Participants who are diagnosed as Lennox-Gastaut syndrome with tonic/atonic seizures and atypical absence seizures (A history of atypical absence seizures will also be incorporated). 2. Participants who had a slow spike-and-wave pattern in an electroencephalogram within 6 months prior to the enrollment for the Observation Period. 3. Participants who had at least a total of 90 seizures in the 28 days prior to the enrollment for the Observation Period. 4. Participants who have been on 1 - 3 anti-epileptic drugs from 28 days prior to the enrollment for the Observation Period and have not changed the type of the anti-epileptic drugs. 5. Participants who have not changed the type nor the dose or administration of the anti-epileptic drugs they are taking in the Observation Period. Exclusion criteria; 1. Participants who had a history of generalized tonic-clonic status epilepticus within baseline. 2. Participants who received drug therapy at least 4 times to be rescued from status epilepticus within baseline. 3. Participants who had a history of hypoxia which needed emergency resuscitation within 12 months prior to the Treatment Period. 4. Participants who were on a ketogenic diet or have received adrenocorticotropic hormone (ACTH) therapy or Vitamin B6 therapy within 6 months prior to the Treatment Period. 5. Participants who had a history of suicide attempt within the 1 year prior to the Treatment Period. 6. Participants who had a history of or has an allergy to triazole compound. 7. Participants who have clinically significant electrocardiogram abnormalities at baseline. 8. Participants who are pregnant, who may be pregnant, who are lactating or who wish to be pregnant.