A Study to Investigate How Effective, Safe and Tolerable the Drug NBI-921352 is When Used With Anti-seizure Medications in Adults With Focal Onset Seizures

Key Inclusion Criteria:

• Capable of providing consent and has completed the written informed consent.
• Male or female, 18 to 65 years of age, inclusive, with a body mass index (BMI) < 40 kg/m^2.
• Diagnosis of focal onset epilepsy according to the International League Against Epilepsy (ILAE) Classification of Epilepsy (2017) at least 18 months before screening.
• History of uncontrolled seizures despite adequate treatment with at least 1 anti-seizure medication (ASM) for at least 18 months prior to screening.
• Treatment with at least 1 but not more than 4 ASMs for at least 1 month before screening, during the baseline seizure diary data collection, and throughout the duration of the study.
• Be able to keep accurate seizure diaries.
• Documented seizure frequency in the baseline seizure diary of ≥8 countable focal seizures during the 8-week seizure baseline period.

Key Exclusion Criteria:

• History of epilepsy with only nonmotor seizures without an observable component, psychogenic nonepileptic seizures, or primary generalized seizures.
• Presence or previous history of developmental and/or epileptic encephalopathy.
• Presence of seizure types other than FOS.
• Status epilepticus within the last 12 months before enrollment.
• Any suicidal behavior or suicidal ideation of type 4 (active suicidal ideation with some intent to act, without specific plan) or type 5 (active suicidal ideation with specific plan and intent) based on the C-SSRS in the 2 years before screening, a history of suicide attempt in the last 2 years, or more than 1 lifetime suicide attempt.
• Multiple drug allergies or a severe drug reaction to an ASM(s), including dermatological (eg, Stevens-Johnson syndrome), hematological, or organ toxicity reactions.
• An implanted responsive neurostimulator system (RNS).