The X-TOLE3 Phase 3 clinical trial is a randomized, double-blind, placebo-controlled study that will evaluate the clinical efficacy, safety and tolerability of XEN1101 administered as adjunctive therapy in focal-onset seizures.

Approximately 360 subjects will be randomized in a blinded manner to one of two active treatment groups or placebo in a 1:1:1 fashion (XEN1101 25 mg : 15 mg : Placebo). Eligible subjects will have up to 9.5 weeks of baseline to assess frequency of seizures, followed by 12 weeks of blinded treatment. In order to be included in the study, subjects must be treated with a stable dose of 1 to 3 allowable antiseizure medications (ASMs) for at least one month prior to screening, during baseline, and throughout the double-blind treatment period (DBP) of the study. During the DBP, subjects will be instructed to orally take XEN1101 or placebo once daily with an evening meal.

Subjects who complete the 12-week DBP will have the opportunity to qualify and enroll in a separate open-label extension (OLE) study for continued treatment with XEN1101. Subjects who do not enroll in the OLE will enter a 8-week post treatment follow-up period.

Inclusion Criteria:

• Be properly informed of the nature and risks of the study and give informed consent in writing, prior to entering the study
• Diagnosis (≥2 years) of focal epilepsy according to the International League Against Epilepsy (ILAE) Classification of Epilepsy (2017). Subject must have had adequate trials of at least 2 ASMs, which were given (and tolerated) at adequate therapeutic doses, without achieving sustained seizure freedom.
• Treatment with a stable dose of 1 to 3 allowable current ASMs for at least one month prior to screening, during baseline, and throughout the duration of the DBP
• Able to keep accurate seizure diaries

Exclusion Criteria:

• Previously documented electroencephalogram which shows any pattern not consistent with focal etiology of seizures.
• History of focal aware non-motor seizures only, non-epileptic psychogenic seizure, primary generalized seizure, developmental and epileptic encephalopathy, including Lennox-Gastaut syndrome.
• Seizures secondary to drug or alcohol use, ongoing infection, neoplasia, demyelinating disease, degenerative neurological disease, metabolic illness, progressive structural lesion, encephalopathy, or progressive central nervous system (CNS) disease.
• History of status epilepticus or repetitive seizures within the 12-month period preceding Visit 1 where the individual seizures cannot be counted.
• History of neurosurgery for seizures <1 year prior to Visit 1, or radiosurgery <2 years prior to enrollment.
• Any medical condition or personal circumstance that, in the opinion of the investigator, exposes the subject to unacceptable risk by participating in the study or prevents adherence to the protocol.