An AE was defined as any untoward medical occurrence in a clinical investigation participant administered with 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 safety analysis set (SAS) was defined as participants who provided informed consent for the OLE study, received at least 1 dose of perampanel in the OLE study, and had at least 1 postdose safety assessment 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 pre-perampanel baseline was assessed for all partial-onset seizure types. The pre-perampanel baseline was defined as: (1) for participants who had been assigned to placebo treatment in the core DB study, the pre-perampanel baseline was computed from all data during the core DB study, and (2) for participants who had been assigned to perampanel in the core DB study, the pre-perampanel baseline was computed from the pre-randomization phase of the core DB study.

Full Intent-to-treat population (ITT), defined as participants who provided informed consent for the OLE, received at least 1 dose of perampanel in the OLE, and had valid seizure data for overall, Complex Partial Plus Secondarily Generalized Seizures and Secondarily Generalized Seizures arm, respectively during the perampanel treatment duration.

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. The pre-perampanel baseline was defined as: (1) for participants who had been assigned to placebo treatment in the core DB study, the Pre-perampanel baseline was computed from all data during the core Double-Blind (DB) study, and (2) for participants who had been assigned to perampanel in the core DB study, the pre-perampanel baseline was computed from the pre-randomization phase of the core DB study. The data is presented as percent responders.

Full Intent-to-treat population (ITT), defined as participants who provided informed consent for the OLE, received at least 1 dose of perampanel in the OLE, and had valid seizure data for overall, Complex Partial Plus Secondarily Generalized Seizures and Secondarily Generalized Seizures arm, respectively during the perampanel treatment duration.