An AE was defined as any untoward medical occurrence in a clinical investigation participant administered an investigational product. A SAE was defined as any untoward medical occurrence that at any dose resulted in death, was life-threatening (ie, the participant was at immediate risk of death from the AE as it occurred; this did not include an event that, had it occurred in a more severe form or was allowed to continue, might have caused death), required inpatient hospitalization or prolongation of existing hospitalization, resulted in persistent or significant disability/incapacity, or was as a congenital anomaly/birth defect (in the child of a participant who was exposed to the study drug). In this study, treatment emergent AEs (defined as an AE (serious or non-serious) that started/increased in severity on/after the first dose of study medication up to 30 days after the final dose of study medication) were assessed. The data is presented in the safety section of the results.

Safety Analysis Set was defined as participants who received at least 1 dose of open-label perampanel and had at least 1 safety assessment after the first dose of perampanel in the OLE study.

Seizure frequency was derived from information (seizure count and type) recorded in participant diary. The seizure frequency per 28 days was calculated as the number of seizures divided by the number of days in the interval and multiplied by 28. The percent change in 28-day seizure frequency from baseline was assessed for all partial-onset seizures types. For participants who had been assigned to treatment with perampanel (previous treatment), pre-perampanel Baseline referred to the Prerandomization Phase of the Core Double Blind study. For participants who had been assigned to treatment with placebo (previous treatment), pre-perampanel Baseline was computed from all data during the Core Double Blind study (including Prerandomization Phase) prior to treatment with perampanel.

The analysis was based on the Full Intent to Treat (ITT) Analysis Set, defined as participants who received at least 1 dose of open-label perampanel and had valid seizure data during the OLE study.

Seizure frequency was derived from information (seizure count and type) recorded in participant diary. The percentage of participants who experienced a 50% or greater reduction in seizure frequency per 28 days relative to the pre-perampanel Baseline (responders) was assessed. For participants who had been assigned to treatment with perampanel (previous treatment), pre-perampanel Baseline referred to the Prerandomization Phase of the Core Double Blind study. For participants who had been assigned to treatment with placebo (previous treatment), pre-perampanel Baseline was computed from all data during the Core Double Blind study (including Prerandomization Phase) prior to treatment with perampanel. The data is presented as percent responders.

The analysis was based on the Full Intent to Treat (ITT) Analysis Set, defined as participants who received at least 1 dose of open-label perampanel and had valid seizure data during the OLE study.