A Study of the Effectiveness, Safety, and Tolerability of Carisbamate as Add-On Therapy in Patients With Partial Onset Seizures.

Inclusion Criteria: * Diagnosis of partial onset seizures * had a neuroimaging procedure (computed tomography \[CT\] or magnetic resonance imaging \[MRI\] within the past 5 years that excluded a progressive neurologic disorder * History of inadequate response to at least 1 antiepileptic drug * Current treatment with at least 1 and up to 3 antiepileptic drugs. To be eligible for the double-blind treatment phase of study CARISEPY3013, patients must: have at least 6 partial onset seizures during the 56-day baseline period * Have not had \> = 100 partial onset seizures per 28 days in the baseline period * And no seizure-free period of more than 3 weeks during the baseline period. Exclusion Criteria: * History of status epilepticus or epilepsia partialis continua in the 6 months before study entry * Have a generalized epileptic syndrome * have a diagnosis of Lennox-Gastaut Syndrome * Currently experiencing seizures that cannot be counted accurately * have experienced rates of \> = 100 partial onset seizures in any monthly period in the 6 months before study entry * Have a history of any current or past nonepileptic seizures, including psychogenic seizures * History of or current serious or medically unstable systemic disease * evidence of cardiac disease, including unstable angina, myocardial infarction, within the past 2 years, uncontrolled heart failure, major arrhythmias, congenital short QT syndrome, or significant shortening or lengthening of the QTc interval of the electr…