An Open-Label Extension of the Study XEN496 (Ezogabine) in Children With KCNQ2-DEE

An Open-Label Extension of the Study XEN496 in Children With KCNQ2 Developmental and Epileptic Encephalopathy

To assess the long-term safety and tolerability of XEN496 in pediatric subjects with KCNQ2 developmental and epileptic encephalopathy (KCNQ2-DEE) who had participated in the primary study (XPF-009-301).

This is an open-label, long-term extension study of XEN496 for the treatment of seizures in subjects with KCNQ2-DEE, that will be open to eligible subjects who participated in the primary study, XPF-009-301. The primary objective is to assess the long-term safety of XEN496. A double-blind transition/titration period will be used to maintain blinding to the treatment allocation in the primary study (XPF-009-301). After completion of the blinded transition/titration period, subjects will receive the open label study drug at their optimal dose for approximately 35 months.

Inclusion Criteria:

• Subject completed participation in the primary study, XPF-009-301. A subject who withdraws from the primary study due to meeting protocol-specified worsening criteria will be considered as having completed participation in the primary study.
• The caregiver is willing and able to be compliant with diary completion, visit schedule, and study drug administration.
• Subject's caregiver achieved a minimum of 85% compliance with daily diary completion during both baseline and the double-blind period of the primary study.

Exclusion Criteria:

• Any adverse event(s) or serious adverse event(s) during the primary study XPF-009-301, which in the opinion of the investigator and sponsor's medical monitor, would preclude the subject's entry into the OLE study.
• A clinically significant condition or illness, or symptoms other than those resulting from KCNQ2-DEE, present at screening/baseline that, in the opinion of the investigator, would pose a risk to the subject if s/he were to enter the study.
• Any conditions that were specified as exclusion criteria in the primary study, XPF-009-301.
• It is anticipated that the subject will require treatment with at least 1 of the disallowed medications during the study.
• Any change in cardiac rhythm or atrioventricular conduction in the primary study that, in the investigator's opinion, is a significant risk to subject safety.