A Phase 2, Multicenter, Randomized, Double-blind, Placebo-controlled Study to Evaluate the Efficacy, Safety, and Tolerability of TAK-935 (OV935) as an Adjunctive Therapy in Pediatric Participants With Developmental and/or Epileptic Encephalopathies

A Phase 2, Multicenter, Randomized, Double-Blind, Placebo-Controlled Study to Evaluate the Efficacy, Safety, and Tolerability of TAK-935 (OV935) as an Adjunctive Therapy in Pediatric Patients With Developmental and/or Epileptic Encephalopathies

The purpose of this study is to investigate the effect on the frequency of all seizures (convulsive and drop) in participants treated with TAK-935 compared to placebo.

The drug being tested in this study is called TAK-935 (OV935). This randomized, double-blind study will assess the effects of TAK-935 (OV935), compared to placebo, on efficacy, safety, and tolerability in pediatric participants with Dravet syndrome (DS) or Lennox Gastaut syndrome (LGS). This multi-center trial will be conducted worldwide and will enroll approximately 126 participants.

Participants will be randomized based on their diagnosis in 2 categories; DS or LGS. The study will consist of 2 periods: Screening Period and Treatment Period. The overall duration of Treatment Period is up to 20 weeks including 8-week Dose Optimization Period and 12-week Maintenance Period. The overall time to participants in this study is approximately 30 weeks.

Participants completing this study will have an option to enroll in the open-label extension study, under a separate protocol.

Inclusion Criteria:

1. Male and female participants aged greater than or equal to (>=) 2 and less than or equal to (<=) 17 years
2. Clinical diagnosis of DS or LGS
3. Weight of >=10 kilogram (kg) at the Screening visit
4. Currently taking 1 to 4 anti-epileptic drugs (AEDs) at a stable dose
5. Failed to become and remain seizure free with trials of at least 2 AEDs

Exclusion Criteria:

1. Has been admitted to a medical facility and intubated for treatment of status epilepticus 2 or more times in the 3 months immediately prior to the screening visit
2. Non-epileptic events that cannot be reliably distinguished from epileptic seizures
3. Participation in a clinical study involving another study drug in the previous month