Drop seizure was defined as a drop attack or spell involving the entire body, trunk, or head that led to a fall, injury, slumping in a chair, or the participant's head hitting a surface or that could have led to a fall or injury, depending on the participant's position at the time of the attack or spell. A responder was a participant who experienced a 50% or greater reduction in drop seizure frequency per 28 days during Maintenance from prerandomization.

Total seizure was the number of seizures assessed and recorded by the participant's parent/caregiver in the participant seizure diary. Seizure diaries was used to collect seizure counts and types. A responder was a participant who experienced a 50% or greater reduction in drop seizure frequency per 28 days during Maintenance from prerandomization.

Non-drop seizures were defined as non-drop attacks or spells. Drop attacks and spells involved the entire body, trunk, or head and lead to a fall, injury, slumping in a chair, or the participant's head hitting a surface, or could lead to a fall or injury, depending on the participant's position at the time of the attack or spell. Seizure frequency was based on the number of drop seizures per 28 days, calculated as the number of drop seizures over the entire time interval divided by the number of days in the interval and multiplied by 28.

Drop seizure was defined as a drop attack or spell involving the entire body, trunk, or head that led to a fall, injury, slumping in a chair, or the participant's head hitting a surface or that could have led to a fall or injury, depending on the participant's position at the time of the attack or spell. Non-drop seizures were defined as non-drop attacks or spells. Total seizure was the number of seizures assessed and recorded by the participant's parent/caregiver in the participant seizure diary. Seizure diaries were used to collect seizure counts and types. A responder was a participant who experienced a 75% or greater reduction in drop seizure/non-drop seizure/ frequency per 28 days during Maintenance from prerandomization.

Drop seizure was defined as a drop attack or spell involving the entire body, trunk, or head that led to a fall, injury, slumping in a chair, or the participant's head hitting a surface or that could have led to a fall or injury, depending on the participant's position at the time of the attack or spell. Non-drop seizures were defined as non-drop attacks or spells. Total seizure was the number of seizures assessed and recorded by the participant's parent/caregiver in the participant seizure diary. Seizure diaries was used to collect seizure counts and types. A responder was a participant who experienced a 100% or greater reduction in drop seizure/non-drop seizure/ frequency per 28 days during Maintenance from prerandomization.

Non-drop seizures were defined as non-drop attacks or spells. Drop attacks and spells involved the entire body, trunk, or head and lead to a fall, injury, slumping in a chair, or the participant's head hitting a surface, or could lead to a fall or injury, depending on the participant's position at the time of the attack or spell. A responder was a participant who experienced a 50% or greater reduction in non-drop seizure frequency per 28 days during Maintenance from prerandomization.

Assessment of disease severity utilized the CGIC scale at end of treatment to evaluate participants change in disease status from baseline. The CGIC is a 7-point likert scale that measures a physician's global impression of a participants clinical condition. Scale ranged from 1 to 7 with lower score indicated improvement (1=very much improved, 2=much improved, 3=minimally improved), higher score indicated worsening (5=minimally worse, 6= much worse, 7=very much worse), and a score of 4 indicated no change.

A TEAE was defined as an adverse event with an onset date, or a worsening in severity from baseline (pre-treatment), on or after the first dose of study drug up to 28 days following study drug discontinuation. An AE was defined as any untoward medical occurrence in a participant or clinical investigation in a participant administered an investigational product. An AE does not necessarily have a causal relationship with a medicinal product. A serious adverse event (SAE) was defined as any AE if it resulted in death or life-threatening AE or required inpatient hospitalization or prolongation of existing hospitalization or resulted in persistent or significant incapacity or substantial disruption of the ability to conduct normal life functions or was a congenital anomaly/birth defect.

Treatment-emergent markedly abnormal value for laboratory values was based Common Terminology Criteria for Adverse events (CTCAE) Version 4.0, and determined as if the post baseline CTCAE Version 4.0 grade increases from baseline and the post baseline grade was >=2 (>=3 for phosphate). Laboratory tests included: Hematology count with differential, Chemistry (Electrolytes, Liver function tests, Renal function parameters, Other: albumin, calcium, cholesterol, globulin, glucose, lactate dehydrogenase, phosphorus, total protein, lipid panel, uric acid), Urinalysis, and Viral tests (Hepatitis B surface antigen, Hepatitis C).

Clinically significant means that a value must have met both the criterion value and satisfied the magnitude of change relative to baseline. Vital sign parameters included systolic blood pressure (BP), diastolic BP, pulse rate.

Due to the early termination of the study resulting in reduced sample size and the variability in treatment response, population pharmacokinetic (PK) analysis and population pharmacokinetic/pharmacodynamic (PK/PD) modeling planned for this study were not conducted and hence data was not collected and analyzed for this outcome measure.

Participants received starting dose of perampanel, one 2 milligram (mg) oral tablet or 4 milliliter (mL) oral suspension (containing 2 mg perampanel), once daily at bedtime then up-titrated weekly in 2 mg increments to a target dose of 8 milligram per day (mg/day) during titration period. During the maintenance period, participants continued to receive the perampanel dose level that was administered at the end of the titration period. The total duration of the titration period (6 weeks) and maintenance period (12 weeks) in the Core Study Phase was 18 weeks.

Participants who completed the Core Study Phase and who were eligible entered into Extension Phase A. Participants previously assigned to perampanel arm (Core Study Phase) continued taking study medication at the dose received during the Core maintenance period, and participants previously assigned to a placebo arm (Core Study Phase) started perampanel dose as one 2 mg tablet or 4 mL oral suspension (containing 2 mg perampanel) once daily at bedtime, then up-titrated weekly in 2-mg increments up to a maximum dose of 8 mg/day for 6 weeks conversion period of Extension Phase A. After the conversion period, participants could be titrated up to 12 mg/day in 2-week intervals during the maintenance period (46 weeks) of Extension Phase A as per the investigator's discretion. The total duration of the conversion period and maintenance period in Extension Phase A was 52 weeks.

Participants who completed Extension Phase A and who were eligible entered into Extension Phase B. Participants received perampanel at their optimal perampanel dose (that is, dose maintained at the end of Extension A) until perampanel was available commercially or accessible via extended access program (EAP) (in the country in which a participant resides) or unless study termination by the sponsor (up to 188 weeks).

Participants received starting dose of perampanel, one 2 mg oral tablet or 4 mL oral suspension (containing 2 mg perampanel), once daily at bedtime then up-titrated weekly in 2 mg increments to a target dose of 8 mg/day during titration period. During the maintenance period, participants continued to receive the perampanel dose level that was administered at the end of the titration period. The total duration of the titration period (6 weeks) and maintenance period (12 weeks) in the Core Study Phase was 18 weeks.

Participants received starting dose of perampanel, one 2 mg oral tablet or 4 mL oral suspension (containing 2 mg perampanel), once daily at bedtime then up-titrated weekly in 2 mg increments to a target dose of 8 mg/day during titration period. During the maintenance period, participants continued to receive the perampanel dose level that was administered at the end of the titration period. The total duration of the titration period (6 weeks) and maintenance period (12 weeks) in the Core Study Phase was 18 weeks.

Participants received starting dose of perampanel, one 2 mg oral tablet or 4 mL oral suspension (containing 2 mg perampanel), once daily at bedtime then up-titrated weekly in 2 mg increments to a target dose of 8 mg/day during titration period. During the maintenance period, participants continued to receive the perampanel dose level that was administered at the end of the titration period. The total duration of the titration period (6 weeks) and maintenance period (12 weeks) in the Core Study Phase was 18 weeks.

Participants who completed Core Study and who were eligible entered Extension A. Participants who received perampanel in Core Study, continued at dose received during Core maintenance period, and participants who received placebo in Core Study started perampanel dose as one 2 mg oral tablet or 4 mL oral suspension (containing 2 mg perampanel) once daily at bedtime, then up-titrated weekly in 2-mg increments up to dose of 8 mg/day for 6 weeks conversion period. After conversion period, participants could be titrated up to 12 mg/day in 2-week intervals during maintenance period (46 weeks) as per investigator's discretion. Total duration of conversion and maintenance period in Extension Phase A was 52 weeks. Participants who completed Extension A and who were eligible entered into Extension B in countries where extended access program (EAP) could not be implemented, and received perampanel at optimal dose (dose at end of Extension A) until perampanel was available commercially or unless study termination (up to 188 weeks).

Participants received starting dose of perampanel, one 2 mg oral tablet or 4 mL oral suspension (containing 2 mg perampanel), once daily at bedtime then up-titrated weekly in 2 mg increments to a target dose of 8 mg/day during titration period. During the maintenance period, participants continued to receive the perampanel dose level that was administered at the end of the titration period. The total duration of the titration period (6 weeks) and maintenance period (12 weeks) in the Core Study Phase was 18 weeks.

Participants who completed Core Study and who were eligible entered Extension A. Participants who received perampanel in Core Study, continued at dose received during Core maintenance period, and participants who received placebo in Core Study started perampanel dose as one 2 mg oral tablet or 4 mL oral suspension (containing 2 mg perampanel) once daily at bedtime, then up-titrated weekly in 2-mg increments up to dose of 8 mg/day for 6 weeks conversion period. After conversion period, participants could be titrated up to 12 mg/day in 2-week intervals during maintenance period (46 weeks) as per investigator's discretion. Total duration of conversion and maintenance period in Extension Phase A was 52 weeks. Participants who completed Extension A and who were eligible entered into Extension B in countries where extended access program (EAP) could not be implemented, and received perampanel at optimal dose (dose at end of Extension A) until perampanel was available commercially or unless study termination (up to 188 weeks).

Participants who completed Core Study and who were eligible entered Extension A. Participants who received perampanel in Core Study, continued at dose received during Core maintenance period, and participants who received placebo in Core Study started perampanel dose as one 2 mg oral tablet or 4 mL oral suspension (containing 2 mg perampanel) once daily at bedtime, then up-titrated weekly in 2-mg increments up to dose of 8 mg/day for 6 weeks conversion period. After conversion period, participants could be titrated up to 12 mg/day in 2-week intervals during maintenance period (46 weeks) as per investigator's discretion. Total duration of conversion and maintenance period in Extension Phase A was 52 weeks. Participants who completed Extension A and who were eligible entered into Extension B in countries where extended access program (EAP) could not be implemented, and received perampanel at optimal dose (dose at end of Extension A) until perampanel was available commercially or unless study termination (up to 188 weeks).