Seizure frequency per 28 days was derived from the information recorded in the participant diaries. PGTC seizure frequency per 28 days was calculated as the number of PGTC seizures divided by the number of days in the interval and multiplied by 28. The percent change in seizure frequency relative to baseline (prerandomization) for primary generalized seizure subtype (myoclonic and absence) per 28 days during the Titration and Maintenance Periods combined was analyzed.

All seizures included PGTC, myoclonic, absence and all other seizures that occur during the study. A responder was a participant who experienced a 50% or greater reduction in seizure frequency per 28 days during Maintenance- LOCF from prerandomization. The data was presented as percentage of participants.

Primary generalized seizure subtype included absence and myoclonic seizures. A responder was a participant who experienced a 50% or greater reduction in seizure frequency per 28 days during Maintenance - (LOCF) from prerandomization. The data was presented as the percentage of participants.

Week 1 began on the date of first dose of the perampanel treatment regardless of whether it occurred in the Core Study or Extension Phase and continued to and included the date of the last dose of perampanel in the Extension Phase. For any given analysis window and seizure type(s), a 50% responder from Core Study Randomization is a participant whose seizure frequency per 28 days for that seizure type(s) during that analysis window is 50% to 100% lower than his or her Core Study Prerandomization baseline seizure frequency per 28 days for that same seizure type(s). In Part B of the Extension Phase (after Visit 15), the seizure diary is only completed for days on which a seizure occurred and missing days were imputed as non-seizure days.

Efficacy assessments included seizure counts from participant diaries. The percent change in seizure frequency was assessed during the perampanel treatment duration, with the pre-perampanel baseline being used for evaluating the change. The pre-perampanel baseline was defined as follows: 1) for all participants who had been assigned to placebo treatment in the Core Study, the pre-perampanel baseline was computed from all valid seizure diary data during the Core Study, and 2) for participants who had been assigned to perampanel in the Core Study, the pre-perampanel baseline was computed from all valid seizure diary data during the Prerandomization Phase plus the 4 weeks prior to the Prerandomization Phase of the Core Study. The perampanel treatment duration consisted of: 1) the Randomization Phase of the Core Study plus the Extension Phase for participants assigned to perampanel in the Core Study, and 2) the Extension Phase for participants assigned to placebo in the Core Study.

An Adverse event (AE) was defined as any untoward medical occurrence in a clinical investigation participant administered an investigational product. A serious adverse event (SAE) was defined as any untoward medical occurrence that at any dose resulted in death, was life-threatening (i.e., the subject 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 a congenital anomaly/birth defect (in the child of a subject who was exposed to the study drug). In this study, treatment emergent adverse events (TEAEs) (defined as an AE 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.

Total of all reporting groups

Participants received 6 tablets (initially ,1 tablet of 2 mg perampanel plus 5 tablets of perampanel matched placebo) and up-titrated weekly in 2 mg increments to a target dose range of 8 mg per day maintaining the blind with administration of 6 tablets per day of either perampanel/perampanel matched placebo.

A responder was a participant who experienced a 50% or greater reduction in seizure frequency per 28 days during Maintenance-last observation carried forward (LOCF) from prerandomization. The data was presented as the percentage of participants.

Full Analysis Set included all randomized participants who received as least 1 dose of study drug and had any postbaseline seizure frequency data. Last observation carried forward (LOCF).

Responder rate was defined as the percentage of participants who experienced a 50% or greater reduction in PGTC and total seizure frequency during treatment per 28 days relative to baseline (responder). Week 1 began on the date of first dose of the perampanel treatment regardless of whether it occurred in the Core Study or Extension Phase and continued to and included the date of the last dose of perampanel in the Extension Phase. For any given analysis window and seizure type(s), a 50% response from Core Study Prerandomization is a participant whose seizure frequency per 28 days for that seizure type(s) during that analysis window is 50% to 100% lower than his or her Core Study Prerandomization baseline seizure frequency per 28 days for that same seizure type(s). In Part B of the Extension Phase (after Visit 15), the seizure diary is only completed for days on which a seizure occurred and missing days were imputed as non-seizure days.

The Extension Phase FAS included participants who were eligible to participate in the Extension Phase, received at least 1 dose of study drug in this phase, and had baseline seizure frequency data and at least 1 observation of valid seizure diary data during study drug treatment duration.

Seizure frequency per 28 days was derived from the information recorded in the participant diaries. PGTC seizure frequency per 28 days was calculated as the number of PGTC seizures divided by the number of days in the interval and multiplied by 28. The percent change in seizure frequency relative to baseline (prerandomization) for all seizures (PGTC, myoclonic, absence and all other seizures that occur during the study) per 28 days during the Titration and Maintenance Periods combined was analyzed.

Full Analysis Set

Seizure frequency per 28 days was derived from the information recorded in the participant diaries. PGTC seizure frequency per 28 days was calculated as the number of PGTC seizures divided by the number of days in the interval and multiplied by 28. The percent change in seizure frequency relative to baseline (prerandomization) for primary generalized seizure subtype (myoclonic and absence) per 28 days during the Titration and Maintenance Periods combined was analyzed.

Full Analysis Set

All seizures included PGTC, myoclonic, absence and all other seizures that occur during the study. A responder was a participant who experienced a 50% or greater reduction in seizure frequency per 28 days during Maintenance- LOCF from prerandomization. The data was presented as percentage of participants.

Full Analysis Set

Primary generalized seizure subtype included absence and myoclonic seizures. A responder was a participant who experienced a 50% or greater reduction in seizure frequency per 28 days during Maintenance - (LOCF) from prerandomization. The data was presented as the percentage of participants.

Only a subset of participants in the Full Analysis Set who experienced these seizure types during the Prerandomization Phase of the study were included in this analysis.

Week 1 began on the date of first dose of the perampanel treatment regardless of whether it occurred in the Core Study or Extension Phase and continued to and included the date of the last dose of perampanel in the Extension Phase. For any given analysis window and seizure type(s), a 50% responder from Core Study Randomization is a participant whose seizure frequency per 28 days for that seizure type(s) during that analysis window is 50% to 100% lower than his or her Core Study Prerandomization baseline seizure frequency per 28 days for that same seizure type(s). In Part B of the Extension Phase (after Visit 15), the seizure diary is only completed for days on which a seizure occurred and missing days were imputed as non-seizure days.

Full analysis set included all participants who were eligible to participate in the Extension Phase, received at least 1 dose of perampanel in this phase, and had baseline seizure frequency data and at least 1 observation of valid seizure diary data during the perampanel treatment duration.

Efficacy assessments included seizure counts from participant diaries. The percent change in seizure frequency was assessed during the perampanel treatment duration, with the pre-perampanel baseline being used for evaluating the change. The pre-perampanel baseline was defined as follows: 1) for all participants who had been assigned to placebo treatment in the Core Study, the pre-perampanel baseline was computed from all valid seizure diary data during the Core Study, and 2) for participants who had been assigned to perampanel in the Core Study, the pre-perampanel baseline was computed from all valid seizure diary data during the Prerandomization Phase plus the 4 weeks prior to the Prerandomization Phase of the Core Study. The perampanel treatment duration consisted of: 1) the Randomization Phase of the Core Study plus the Extension Phase for participants assigned to perampanel in the Core Study, and 2) the Extension Phase for participants assigned to placebo in the Core Study.

Full Analysis Set, which comprised all participants who were eligible to participate in the Extension Phase, received at least 1 dose of perampanel in this phase, and had baseline seizure frequency data and at least 1 observation of valid seizure diary data during the perampanel treatment duration.

An Adverse event (AE) was defined as any untoward medical occurrence in a clinical investigation participant administered an investigational product. A serious adverse event (SAE) was defined as any untoward medical occurrence that at any dose resulted in death, was life-threatening (i.e., the subject 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 a congenital anomaly/birth defect (in the child of a subject who was exposed to the study drug). In this study, treatment emergent adverse events (TEAEs) (defined as an AE 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 included participants who were randomized to study drug, received at least 1 dose of study drug, and had at least 1 postbaseline safety assessment.

Participants received 6 tablets (initially ,1 tablet of 2 mg perampanel plus 5 tablets of perampanel matched placebo) and up-titrated weekly in 2 mg increments to a target dose range of 8 mg per day maintaining the blind with administration of 6 tablets per day of either perampanel/perampanel matched placebo.

The Extension Phase consisted of two parts: Part A (6-week blinded Conversion Period plus a 32-week Maintenance Period) and Part B (maximum of 104-week Maintenance Period), which was followed by an additional 4-week Follow-up Period. Part A: Participants who were assigned to the perampanel arm in the Core Study continued to receive blinded perampanel once daily at the dose received during the Maintenance Period of the Core Study. During the Conversion Period, dose adjustments could be made at the investigator's discretion. Part B: Participants were unblinded to study treatment and remained on the optimal perampanel dose established during the blinded Conversion Period (Part A). Dose adjustment in 2-mg increments (upwards or downwards) was allowed at the investigator's discretion. Participants who could not tolerate a dose of 2 mg/day perampanel during the Extension Period were discontinued from the study. The maximum dose of perampanel allowed during the Extension Phase was 12 mg/day.

Median Difference to Placebo for Myoclonic Seizure