A Study to Evaluate XEN1101 as Adjunctive Therapy in Primary Generalized Tonic-Clonic Seizures

This is a Phase 3, multicenter, randomized, double-blind, placebo-controlled study to evaluate the clinical efficacy, safety, and tolerability of XEN1101 administered as adjunctive treatment in subjects diagnosed with generalized epilepsy and experiencing probable or possible PGTCS (with or without other subtypes of generalized seizures), and taking 1 to 3 anti-seizure medications (ASMs). Eligible subjects will be randomly assigned 1:1 to XEN1101 or placebo: subjects aged ≥ 18 years will receive XEN1101 25 mg or placebo, and subjects aged ≥12 years and \<18 years will receive either XEN1101 15 mg, 25 mg, or placebo. Randomization will be stratified based on region, age group, and background use of CYP3A4-inducer ASMs. Eligible subjects will have up to 9.5 weeks durations to assess the baseline frequency of seizures, followed by a double-blind treatment period (DBP) where subjects will receive 12 weeks of blinded treatment. 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 enroll in a separate open-label-extension (OLE) study for continued treatment with XEN1101. Subjects who do not enroll in the OLE will enter an 8-week post-treatment follow-up period.