Participants started the study with the dose that they were receiving at the end of their participation in the previously participated Study E2007-G000-332 (Study 332) [NCT02307578]. Doses of perampanel were allowed to be adjusted based on clinical judgment. A minimum perampanel dose of 2 milligram (mg) per day was required to continue in the study. The maximum daily dose of perampanel permitted was 12 mg per day.

Perampanel 2 mg tablets. Doses of perampanel can be adjusted based on clinical judgment. A minimum perampanel dose of 2 mg per day is required to continue in the study. The maximum daily dose of perampanel permitted will be 12 mg per day.

Safety was assessed by monitoring adverse events (AEs), withdrawal from treatment, clinical laboratory tests (chemistry), vital signs, and weight. TEAEs were defined as AEs that emerged from the first dose of study drug to the last visit of Study 341 or on or after 30 days since the last dose of study drug in Study 341, whichever comes later, having been absent at pretreatment (Baseline of Study 332). A markedly abnormal clinical chemistry laboratory value was defined as a laboratory result that worsened in severity to meet modified National Cancer Institute (NCI) toxicity criteria of Grade 2 or higher on treatment. Treatment-related TEAEs were defined as AEs that were considered by the investigator to be possibly or probably related to study treatment. SAEs were defined as any untoward medical occurrence that at any dose; resulted in death, disability/incapacity, birth defect, required inpatient hospitalization or prolongation of existing hospitalization, or was life-threatening.