A Study of a Drug to be Used in Addition With Another Drug to Treat Adults With Uncontrolled Partial-onset Seizures

Inclusion Criteria

• Male or female subjects ≥ 18 years of age.
• Subject is willing and able to sign informed consent.
• Subject has a documented diagnosis of epilepsy with simple POS with a motor component or complex POS with or without secondarily generalized seizures as defined in the Classification of Seizures of the International League Against Epilepsy
• Subject has a documented electroencephalogram within 10 years prior to screening.
• Subject has had at least 3 POS during previous six months.
• Subject has had a sufficient number of seizures at time of enrollment to justify adjunctive therapy, as determined by the Investigator.
• Subjects are required to be ESL-naïve AND
• Maintained on a stable LEV or LTG regimen for at least 1 month (28 days) prior to screening with no history of adjunctive treatment (for Arm 1, ESL as first add-on).

OR

• Maintained on a stable dose of 1-2 AEDs (excluding OXC) for at least 1 month (28 days) prior to screening and who have had prior adjunctive treatment (for Arm 2, ESL as later add-on).
• If the subject is treated with any stimulation device for epilepsy Vagal Nerve Stimulation (VNS), Responsive Neurostimulator (RNS), or similar, the device must have been implanted at least 6 months before screening and the device parameters must be documented as stable for at least 1 month prior to screening. (Note: These devices will not be counted as concomitant AED).
• Except for epilepsy, subject is judged to be in general good health based on medical history, physical examination findings, and clinical laboratory

Exclusion Criteria

• Subjects with a prior exposure to ESL.
• Subjects currently being treated with OXC.
• Subject with a history of allergic reaction to OXC or CBZ, or a history of serious allergic reaction (Stevens-Johnson syndrome, Drug Reaction with Eosinophilia and Systemic Symptoms or similar) to any AED, or a history of serious allergic reactions to other medications.
• Subjects who have taken warfarin, felbamate, vigabatrin, or perampanel, (unless at stable dose with safety testing for ≥ 1 year) within a 4-week period prior to screening.
• Subjects taking ezogabine

.

• Subject has taken any medication prohibited for this protocol within 4 weeks prior to Screening
• Subjects using benzodiazepines on more than an occasional basis (defined as more than 2 times per week), except when used chronically as an AED
• Seizure disorder characterized primarily by simple POS without motor signs.
• Subject has a history of primarily generalized seizures (eg, myoclonic, absence, tonic).
• Subject has a history of status epilepticus or cluster seizures (ie, 3 or more seizures within 30 minutes) within the 3 months prior to screening.
• Subject has had seizures of psychogenic origin or purely subjective seizures within the last 2 years.
• Subject has had seizures too close to count accurately.
• Subject has a known progressive structural central nervous system (CNS) lesion, progressive encephalopathy or any other condition that may result in epilepsy secondary to a cerebral abnormality.
• Subject whose current seizures are related to an acute medical illness or other non-epileptic origin.
• Subjects of Asian ancestry will be excluded if they are carriers of HLA-B*1502. Either:
• Subject must give written informed consent for genotyping, and test negative. OR
• Subjects must provide documentation of prior testing confirming non-carrier status.
• Subject has a major medical illness other than epilepsy that would prevent safe participation in this study, at the discretion of the Investigator, including (but not limited to) cardiac disease, thyroid disease, hepatic or renal impairment, endocrine or metabolic disease, gastrointestinal disease, or hematologic disease. Note: Active medical conditions that are minor or well-controlled are not exclusionary if they do not affect risk to the subject or the study results. If the effect of the condition in regard