Perampanel as Adjunctive Therapy in Pediatrics With Partial Onset Seizures or Primary Generalized Tonic Clonic Seizures

This is an open-label, multicenter study with an Extension Phase to evaluate the safety and tolerability of perampanel oral suspension when administered as an adjunctive therapy in children (ages 4 to less than \[\<\] 12 years) with inadequately controlled partial onset seizures (POS) or primary generalized tonic clonic (PGTC) seizures.

This is a multicenter, open-label, single-arm study in children (age 4 to \<12 years) with inadequately controlled POS or PGTC seizures. The study will consist of a Core Phase and two Extension Phases (Extension Phase A \[for all countries in the study\], and Extension Phase B \[available for participants enrolled in Japan and in countries where an extended access program {EAP} cannot be implemented, after completion of Extension Phase A\]). The Core Phase will consist of the following 2 phases: Pretreatment and Treatment Phase. The Pretreatment Phase, during which participants will be assessed for eligibility, will consist of up to a 4-weeks +/- 3 days Screening/Baseline Period. The Treatment Phase will consist of 3 periods: Titration Period (up to an 11-weeks: dose titration on the basis of individual clinical response and tolerability), Maintenance Period (up to a 12-weeks: continuation of perampanel oral suspension once daily at the dose level achieved at the end of the Titration Period), and Follow-up Period (up to 4-weeks +/- 7 days: only for those participants not entering into Extension Phase A or those who prematurely discontinue from the study). Extension Phase A will consist of up to 29-weeks Maintenance Period and up to 4-weeks +/- 7 days Follow-up Period after the last dose of perampanel only for participants who did not enter into Extension Phase B. All participants who complete all scheduled visits up to and including Visit 9 in the Treatment Phase will be eligible to participate in Extension Phase A of the study. During the Maintenance Period of Extension Phase A, all participants will continue with their optimal perampanel dose (that is, dose level that they complete on during the Core Phase). After completing Extension Phase A, participants in Japan and in countries where EAP cannot be implemented, participants will be eligible to participate in Extension Phase B. In Japan, treatment will continue as long as clinically appropriate according to the judgment of the investigator. However, treatment of participants in Extension B will be completed when the participant reaches 12 years of age or when perampanel is commercially available in Japan for treatment of POS in pediatric participants (4 to less than 12 years of age). In countries where an EAP cannot be implemented, participation in Extension B will continue as long as clinically appropriate according to the judgment of the investigator, until the participants reaches 12 years of age or perampanel oral suspension is commercially available.

Eligibility Criteria:
Inclusion Criteria:

* Have a diagnosis of epilepsy with POS with or without secondarily generalized (SG) seizures or PGTC seizures according to the International League Against Epilepsy's (ILAE) Classification of Epileptic Seizures (1981). A diagnosis should have been established at least 6 months prior to Visit 1 by clinical history and an electroencephalogram (EEG) that is consistent with the diagnosis; normal interictal EEGs will be allowed provided that the participant meets the other diagnosis criterion (that is, clinical history)
* Male or female participant, from age 4 to \<12 years at the time of informed consent/assent
* Have a minimum weight of 16 kilograms (kg) (35 pounds \[lb\])
* Have had a brain imaging (example, magnetic resonance imaging \[MRI\] scan or computed tomography \[CT\] before Visit 1 that ruled out a progressive cause of epilepsy)
* During the 12 weeks +/- 3 days (4 weeks +/- 3 days in Japan only) prior to Visit 2, participants must have equal or greater than (=\>) one POS or one PGTC seizure. Only simple POS with motor signs, complex POS, and complex POS with secondary generalization are counted toward this inclusion for POS
* Are currently being treated with stable doses of 1 to a maximum of 3 approved antiepileptic drugs (AEDs). Doses must be stable for at least 4 weeks before to Visit 1; in the case where a new AED regimen has been initiated for a participant, the dose must be stable for at least 8 weeks prior to Visit 1. Only one EIAED (defined as carbamazepine, phenytoin, oxcarbazepine, or eslicarbazepine) out of the maximum of three AEDs is allowed (A vagal nerve stimulator \[VNS\] will be counted as one of the 3 allowed AEDs)

Exclusion Criteria:

* Females who are breastfeeding or pregnant at Screening or Baseline (as documented by a positive beta human chorionic gonadotropin \[β-hCG\] or human chorionic gonadotropin \[hCG\] test with a minimum sensitivity of 25 International Units per liter \[IU/L\] or equivalent units of β-hCG or hCG). A separate baseline assessment is required if a negative screening pregnancy test was obtained more than 72 hours before the first dose of study drug
* Females of childbearing potential who:

  * Had unprotected sexual intercourse within 30 days before study entry and who do not agree to use a highly effective method of contraception (example, total abstinence, an intrauterine device, a contraceptive implant, an oral contraceptive, or have a vasectomized partner with confirmed azoospermia) throughout the entire study period or for 28 days after study drug discontinuation. If a highly effective method is not appropriate or acceptable for the participant, then the participant may use a medically effective method (example, a double barrier method such as condom plus diaphragm with spermicide)
  * Are currently abstinent, and do not agree to use a double-barrier method (as described above) or refrain from being sexually active during the study period or for 28 days after study drug discontinuation
  * Are using hormonal contraceptives but are not on a stable dose of the same hormonal contraceptive product for at least 4 weeks before dosing and who do not agree to use the same contraceptive during the study or for 28 days after study drug discontinuation
* Current or history of pseudo-seizures (psychogenic nonepileptic seizures) within approximately 5 years before Visit 1
* Have a history of status epilepticus that required hospitalization during the 6 months before Visit 1
* Have an unstable psychiatric diagnosis that may confound participants' ability to participate in the study or that may prevent completion of the protocol-specified tests (example, significant suicide risk, including suicidal behavior and ideation within 6 months before Visit 1, current psychotic disorder, acute mania)
* Any suicidal ideation with intent with or without a plan within 6 months before Visit 2 (that is, answering "Yes" to questions 4 or 5 on the Suicidal Ideation section of the Columbia Suicide Severity Rating Scale \[C-SSRS\]) in participants aged 6 and above
* Are scheduled and/or confirmed to have epilepsy surgery within 6 months after Visit 1; however, those who have previously documented "failed" epilepsy surgery will be allowed
* Evidence of clinically significant disease (example, cardiac, respiratory, gastrointestinal, renal disease) that in the opinion of the investigator(s) could affect the participant's safety or interfere with the study assessments
* Evidence of moderate or severe renal insufficiency as defined by estimated glomerular filtration rates (eGFRs) of 31 to \<60 milliliters per minute (mL/min) and \<30 mL/min, respectively
* Evidence of significant active hepatic disease. Stable elevation of liver enzymes, alanine aminotransferase (ALT) and aspartate aminotransferase (AST) due to concomitant medication(s), will be allowed if they are less than 3 times the upper limit of normal (ULN)
* Evidence of significant active hematological disease; white blood cell (WBC) count equal or less than (=\<) 2500 per (/) microliter (µL) (2.50 1 constant \[E\]+09/liter \[L\]) or an absolute neutrophil count =\<1000/µL (1.00 1E+09/L)
* Clinically significant electrocardiogram (ECG) abnormality, including prolonged corrected QT interval (QTc) defined as greater than (\>) 450 milliseconds (msec)
* Have a progressive central nervous system (CNS) disease, including degenerative CNS diseases and progressive tumors
* Multiple drug allergies or a severe drug reaction to an AED(s), including dermatological (example, Stevens Johnson syndrome), hematological, or organ toxicity reactions.
* Concomitant use of felbamate as an AED for \<2 years or where the dose has not been stable for at least 8 weeks before Visit 1. Participants must not have a history of WBC count =\<2500/µL, platelets below 100,000, liver function tests (LFTs) above 3 times the ULN, or other indication of hepatic or bone marrow dysfunction while receiving felbamate. If participants received felbamate in the past, it must have been discontinued 8 weeks before Visit 1 to be eligible for study participation
* Concomitant use of vigabatrin: participants who took vigabatrin in the past must be off vigabatrin for at least 5 months before Visit 1 and with documentation showing no evidence of a vigabatrin-associated clinically significant abnormality in a visual perimetry test
* Concomitant use of cannabinoids
* Used benzodiazepines for epilepsy during which the dose has not been stable for \>4 weeks prior to Visit 1. Benzodiazepines use as rescue medication for seizure control is allowed; however, intermittent use of benzodiazepines for any other indication (example, anxiety/sleep disorders) is prohibited
* A VNS implanted \<5 months before Visit 1 or changes in parameter \<4 weeks before Visit 1 (or thereafter during the study)
* On a ketogenic diet for which the diet is not a stable regimen for at least 4 weeks before Visit 1
* History of or a concomitant medical condition that in the opinion of the investigator(s) would preclude the participant's participation in a clinical study or compromise the participant's ability to safely complete the study
* Have previously been exposed to perampanel in a clinical trial or by prescription for more than 2 months or discontinued for Adverse Events (AEs)
* Have participated in a study involving administration of an investigational drug or device within 4 weeks before Visit 1, or within approximately 5 half-lives of the previous investigational compound, whichever is longer
* Participants with rare hereditary problems of galactose intolerance, the Lapp lactase deficiency or glucose-galactose malabsorption