Cenobamate Open-Label Extension Study for YKP3089C025

52 Week Open-Label Safety Study of cenobamate adjunctive therapy for subjects who complete double-blind study YKP3089C025. Subjects will have a 12 week double-blind conversion phase where subjects who received placebo in the double-blind study will be converted to cenobamate. Subjects who received cenobamate in the double-blind study will continue to receive their daily dose of cenobamate. Subjects switching from placebo to cenobamate will be titrated starting at 12.5 mg and increase their dose over the course of 12 weeks as follows 12.5 mg for 2 weeks, 25 mg for two weeks, 50 mg for two weeks, 100 mg for two weeks, 150 mg for two weeks, and 200 mg for two weeks. All subjects will receive 200 mg for the last two weeks of the conversion phase to preserve the blind. After completing the double-blind conversion phase, subjects will have 40 weeks of open-label, flexibly dosed cenobamate. The dose range is 50 mg - 200 mg. Primary endpoints are all safety measures.

Adolescents will follow the same every two week regimen and receive cenobamate as an oral suspension based on weight

Inclusion criteria

• The subject must have successfully completed the Double-blind Treatment Period in the Core study.
• Written informed consent signed by the subject or legal guardian, prior to entering the study, in accordance with the International Council for Harmonisation (ICH) Good Clinical Practice (GCP) guidelines. If the written informed consent is provided by the legal guardian because the subject is unable to do so, a written or verbal assent from the subject must also be obtained. As required by country-specific regulations, only the subject may sign the ICF in accordance with ICH guidelines.

Exclusion criteria

• Subject tests positive, via urine drug screen at Visit 14 of the Core study, for illicit drugs except for tetrahydrocannabinol and Cannabinoids.
• Any significant changes to the subject's medical history that, in the opinion of the Principal Investigator, could affect the subject's safety or conduct of the study.